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Chemisty > Energetics > Flashcards

Energetics Flashcards

1
Q

What is energetics?

A

the energy changes that take place with the surroundings during a chemical reaction

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2
Q

What is an exothermic reaction?

A

reactions that produce heat

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3
Q

Give examples of an exothermic reaction?

A

combustion (burning)

respiration

neutralisation (acid and alkali)

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4
Q

What is an endothermic reaction?

A

reactions that absorb/require heat to occur

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5
Q

Give examples of an endothermic reaction?

A

evaporation (heat the water)

ice cube melting

thermal decomposition

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6
Q

Why is an ice cube melting endothermic?

A

H20 from a solid to a liquid happens from tempratures of 00 to 220

water is melting, absorbing heat

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7
Q

How are exothermic and endothermic reactions represented?

A

they are represented graphically

energy profile diagrams

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8
Q

What is △H (between products)?

A

the difference in energy between the products and reactions in a chemical is known as the energy change △H

H products - H reactants

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9
Q

What does kJ stand for?

A

kilojoules

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10
Q

What does △ stand for?

A

change

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11
Q

What does H stand for?

A

enthalpy

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12
Q

Endothermic reactions have a (positive/negative)△H?

A

positive

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13
Q

Exothermic reactions have a (positive/negative) △H?

A

negative

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14
Q

Why do exothermic reactions have a negative △H?

A

Their products have less energy than their reactants

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15
Q

Why do endothermic reactions have a positive △H?

A

their products have more energy than thier reactants

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16
Q

What is activation energy (EA)?

A

the minimum amount of energy required between two or more reactants to overcome their mutual repulsion (e.g. two magnets repelling)

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17
Q

What is bond enthalpy (energy)?

A

the average energy required to break one mole of stated bond

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18
Q

Energy is required to (make/break bonds - it is an (exothermic/endothermic) process?

A

Energy is required to break bonds - it is an endothermic process

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19
Q

Energy is (given/taken) when bonds are made - it is an (endothermic/exothermic) process

A

energy is given when bonds are made- it is an exothermic process

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20
Q

Endothermic Profile Diagram

A
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21
Q

Exothermic Profile Diagram

A
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22
Q

Is bond making exothermic or endothermic?

A

exothermic

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23
Q

Is bond breaking endothermic or exothermic?

A

endothemic

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24
Q

What are the three types of △H?

A

△H = H products - H reactants (theoretical)

△H = sum bonds broken - bonds made (theoretical)

△H = mc△T/n (experimental)

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25
Q

What is enthalpy?

A

energy change for a reaction

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26
Q

Is a negative energy change exothermic or endothermic? Why?

A

exothermic

the energy given out when new bonds are made is greater than the energy taken to break the original bonds

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27
Q

Is a positive energy change exothermic or endothermic? Why?

A

endothermic

the energy taken in to break the original bonds is greater than the energy given out when new bonds are made

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28
Q

Exothermic reaction △H is negative/positive?

A

negative

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29
Q

Endothermic reaction △H is negative/positive?

A

positive

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30
Q

In terms of products and reactants why would an endothermic reaction be positive?

A

their products have more energy than their reactants

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31
Q

In terms of products and reactants, why are exothermic reactions negative?

A

their products have less energy than their reactants

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32
Q

How do you measure enthalpy changes for reactions experimentaly?

A

by burning a substance, measuring the temprature change it causes, then calclutaing the enthalpy from the formula

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33
Q

What is the equation for speed?

A

speed = distance/time

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34
Q

What does -1 mean?

A

per something

e.g. 30 m/s or 30 ms-1

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35
Q

What is the equation for a-1

A

1/a

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36
Q

What do all combustion experiments have in common?

A

they are all exothermic and therefore have a negative Q ( heat released)

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37
Q

How do you carry out an energy of different types of alcohol combustion experiment?

A

a known mass of fuel is burned in a spirit burner and the temprature rise of the known mass of water is measured

from this you calculate the energy given out by the fuel in kJ per gram

from your results you will compare the relative values obtained

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38
Q

In the different types of alcohol combustion experiment which is

a) the independant variable
b) the dependant variable
c) the continuos variable

A

a) the type of alcohol
b) temprature of water
c) mass difference of burner

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39
Q

If the temprature of 4.18 kJ per Kg per K, what does this mean?

A

it takes 4.18 Joules of energy to raise one Kg of water by one Kelvin. one Kelvin is equivalent to 0C

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40
Q

How is the mass of fuel burned calculated?

A

measure the mass of the burner before and after the experiment and then calculate the difference

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41
Q

In the differnet types of alcohol combustion experiment what could be sources of error?

A

scale error

human error

heat is lost to the surroundings (out of our control)

can’t burn all alcohol

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42
Q

Why do differnet fuels have different energies of combustion?

A

some react better with oxygen

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43
Q

What does equilibrium mean?

A

balance

in a chemical equilibrium, the concentration of reactants and products do not change

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44
Q

What is static equilibrium?

A

once equilibrium is reached there is not more movement

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45
Q

What is dynamic equilibrium?

A

when the rate (speed) of the fowards reaction is equal to the rate of the reverse, so the net change is 0

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46
Q

What two things does a dynamic equilibrium need?

A

a closed system (closed experiment, no ‘matter’ can be exhanged with the surroundings, occurs in a sealed container)

reversible

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47
Q

Is a phase change a reaction?

A

No but it can still have a dymanic equilibrium

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48
Q

What is the position of equilibrium (P.O.E)?

A

whether the reaction is moving left to right or right to left

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49
Q

What three main factors affect the position of equilibrium/dynamic equilibrium?

A

temprature

concentration of reactants (amounts)

pressure (gases)

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50
Q

What is a system?

A

a chemical reaction

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51
Q

What is Le Chatelier Principle?

A

when a change is exerted on a system in a dynamic equilibrium the position of equilibrium moves to the exact opposite

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52
Q

What would happen if you increased the pressure of reactants?

A

the position of equilibrium would move to the right (more S03)

this is because there are two molecules on the right but three on the left therefore the right has less pressure

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53
Q

What would happen if you increased the temprature?

A

the position of equilibrium would move to the left

this is because the left is the endothermic direction which absorbs heat therefore the amount of product S03 would decrease

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54
Q

What would happen if you increased the concentration of S02 and 02?

A

the position of equilibrium would move right

this is because it wants to remove excess reactants which moves to form products

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55
Q

What can reversible reactions do?

A

go fowards or backwards

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56
Q

In a closed system, a reversible reaction can reach a point of equilibrium. The amount of reactants and products (stays the same/can change). This is becaus the fowards and backward reaction is happening at the (different/same) time (……. equilibrium)

A

stays the same

same time

dynamic

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57
Q

What do strong acids do when dissolved in water?

A

split almost completely into ions when dissolved in water

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58
Q

With weak acids the ions are in what with the undissociated molecules in the acids?

A

equilibrium

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59
Q

Acids are proton (H+) what?

A

donors

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60
Q

Bases are proton (H+) what?

A

acceptors

61
Q

What is a reactant?

A

a substance present at the start of a chemical reaction

62
Q

What is a product?

A

a substance formed in a chemical reaction

63
Q

When reversible reactions reach equilibrium the foward and reverse actions are (still happening/stopping) but at the (same/different) rate so the concentrations of reactants and products (change/do not change)

A

still happening

same

do not change

64
Q

What is a catalyst?

A

changes the rate of chemical reaction without being changed by the reaction itself

65
Q

If we remove the products from an equilibrium mixture, what happens?

A

more reactants are converted into products

66
Q

If a catalyst is used what happns to the equilibrium?

A

it is reached must faster because the catalyst speeds up the reactants and products by the same amount

67
Q

Does a catalyst affect the concentration of reactants and products?

A

no

68
Q

What happens if the foward reaction is exothermic and the temprature is increased?

A

the yield of products is decreased

69
Q

What happens id the foward reaction is exothermic and the temprature is deacreased?

A

the yield of products is increased

70
Q

What will happen if the foward reaction is endothermic and the temprature is increased?

A

the yield of product will increased

71
Q

What will happen if the foward reaction is endothermic and the temprature is decreased?

A

the yield of prduct is decreased

72
Q

What is the equation for Calorimetry?

A
73
Q
A

reversible reaction; goes fowards and backwards at the same time

74
Q
A

-20

75
Q

CHECK

A

-103

76
Q
A

-95

77
Q

CHECK ALL OF THESE

A

-124

78
Q
A

-590

79
Q

An example of an equilibrium problem

A
80
Q

In an experiment, 1.56g of propan-1-ol (CH3CH2CH2OH) was completely burned in air. The heat evolve raised the temprature of 0.250 litres of water from 292.1K to 339.4K. Use this data to calculate the energy of combustion per gram of propan-1-ol (the specific heat capacity of water is 4.18 Jg-1 K-1)

A
81
Q

In an experiment 1.00g of propanone (CH3COCH3) was completely burned in air. The heat evolved raised the temprature of 150g of water from 18.8 to 64.3 0C. Use this data to calculate the energy of combustion per gram of propanone (the specific heat of water is 4.18 Jg-1K-1​)

A
82
Q

50cm3 of 1.0 mol dm-3 hydrochloric acid was added to 50 cm3 of 1.0 mol dm-3 sodium hydrochloric solution. The temprature rose by 6.80C. Calculate the energy of neutralisation for this reaction. Assume that the specific heat capacity of the sloution is 4.18 Jg-1K-1​

A
83
Q

What is reversible reaction?

A

a chemical reaction which can go both ways

the direction of the reaction depends on the condition of the reactants

84
Q

What is a catalyst?

A

a catalyst changes the rate of a chemical reaction without being changed by the reaction itself

85
Q

In the Haber process what are the three raw materials used in the process?

A

natural gas

air

water

86
Q

In the Haber process name a by-product of the process

A

carbon dioxide

87
Q

In the Haber process what could be used to remove this by-product from the mixture of gases?

A

potassium carbonate (alkali)

88
Q

In the Haber process what is the name of the catalyst used?

A

iron

89
Q

The graph shows the yield of ammonia produced at equilibrium under different conditions of temprature and pressure. If the conditions are 200 atmospheres and 4250C, what yield of ammonia is obtained at equilibrium?

CHECK

A

33

90
Q

The graph shows the yield of ammonia produced at equilibrium under different conditions of temprature and pressure. In practice, under the conitions of 200 atmospheres and 425oC, the yield obtained in the plant under these conditions is 15%. Suggest why this is so.

A

the system has not yet reached equilibrium

91
Q

What would be the effect on the yield of ammonia of increasing the pressure? (ammonia is produced at equilibrium under conditions of temprature and pressure)

A

increasing the pressure increases the yield of ammonia

92
Q

Suggest why the Haber process is not operated at even highe pressures.

A

increasing the pressure of gases is expensive

operating at a higher pressure means pipework is more expensive to resist explosion

93
Q

What would be the effect of the yield of ammonia made by the Haber process by decreasing the temprature?

A

lowering the temprature increases the yield

94
Q

Suggest why the Haber process is not operated at even lower temprature

A

lowering the temprature slows down the rate of reactions

95
Q

Use the graph data to explain how ammonia can be removed frim the mixture of gases at atmospheric pressure

A

cool gases below -330C, ammonia liquifies and can be removed

96
Q

The boiling point of these gases atre higher at higher pressure. Use your knowledge of particles to explain this

A

at higher pressure particles are closer together

stronger forces between particles have to be broken down

97
Q

Some of the ammonia is distributed as liquid ammonia by road using tankers. Suggest an advantage of distributing ammoniaa as a liquid rather than as a gas. Use your knowledge of particles in your asnwer

A

In a liquid the oarticles are much closer together

More ammonia can be contained in a given volume

98
Q

The air contains noble gases such as argon. What happens to these noble gases during the process?

A

Noble gases are not reacted and, as unreacted gases are re-cycled, their concentrations will build up

99
Q

Describe the conditions used in the Haber process to increase the rate of reaction

A
100
Q

Describe and explain the conditions used in the manufacture of ammonia to increase the yield

A
101
Q

What is the Haber process used to do?

A

to make NH3 (l)

ammonia (alkali)

102
Q

What can ammonia be used for?

A

fertilisers

103
Q

Why do you need a compromise temprature in the Haber process?

A

the foward reaction is exothermic - the yield of product at equilibrium is increased at lower tempratures

if the temprature is too low the rate of reaction will be too low making the process uneconomical

a compromise is chosen - low enough to get a good yield of ammonia but high enough to obtain a reasonable rate of reaction

104
Q

What catalyst is used in the Haber process reaction and what affect does it have?

A

iron filings - Fe

it does not affect the position of equilibrium but does affect the rate of reaction

ammonia is produced in a shorter time, reducing the cost of the process

iron is a cheap catalyst

105
Q

How is the ammonia taken from the Haber process and why?

A

in its cool state it is tapped off as it is formed otherwise the equilibrium would move to the left

106
Q

How much ammonia is produced from the Haber process?

A

yield = 18%

107
Q

What is the pressure of the Haber process?

A

200-250 atmospheres

(we’re under 1 atmosphere)

108
Q

What is the tenprture of a Haber process?

A

4500C

109
Q

What is the Haber process reaction?

A
110
Q

What is a molecule?

A

a molecule is a collection of two or more atoms held together by chemical bonds - the fundamental unit of compounds

111
Q

How many molecules are on each side of the Haber process?

A

left - 1+3 = 4 molecules of gas

right - 2 molecules of gas

112
Q

What will happen if the pressure is increased in the Haber process?

A

an increase in pressure will make the position of equilibrium move to the reaction which produces the smallest number of molecules

in the Haber process this is the forward reaction

more ammonia is produced

113
Q

Why is the pressure only so high?

A

there is a limit to the pressure which can be used industrially

high pressures require very storng and expensive quiptment

114
Q

Explain the choice of high pressure for the Haber process?

A

a compromise is chosen

high enough to get a good yielf of ammonia

low enough that it wouldn’t add to much to the costs of the process

115
Q

is burning petrol in a car exothermic or endothermic?

A

exothermic

116
Q

is respiration in living cells exothermic or endothermic?

A

exothermic

117
Q

is heating water to make it boil exothermic or endothermic?

A

endothermic

118
Q

is thermal decomposition of limestone into limes and CO2 exothermic or endothermic?

A

endothermic

119
Q

is the reaction of magnesium with oxygen exothermic or endothermic?

A

exothermic

120
Q

when heated continuously, pink cobalt chloride cyrstals can be changed into blue crystals

CoCl2 • 6H2O (pink) ⇌ CoCL2 • 2H2O + 4H2O (blue)

the symbol ⇌ tells you that the reaction is reversible

the pink cobalt chloride cyrstals have water trapped inside their crystal structure

blue cobalt chloride crystals have less water trapped insdie their crystals

how can you tell that the reaction to produce blue crystals is endothermic?

A

moving to oppose change pink to blue

121
Q

when heated continuously, pink cobalt chloride cyrstals can be changed into blue crystals

CoCl2 • 6H2O (pink) ⇌ CoCL2 • 2H2O + 4H2O (blue)

the symbol ⇌ tells you that the reaction is reversible

the pink cobalt chloride cyrstals have water trapped inside their crystal structure

blue cobalt chloride crystals have less water trapped insdie their crystals

how could you change the blue crystals to pink cyrstals?

A

cool down (heat goes foward)

use an ice bath

122
Q

when heated continuously, pink cobalt chloride cyrstals can be changed into blue crystals

CoCl2 • 6H2O (pink) ⇌ CoCL2 • 2H2O + 4H2O (blue)

the symbol ⇌ tells you that the reaction is reversible

the pink cobalt chloride cyrstals have water trapped inside their crystal structure

blue cobalt chloride crystals have less water trapped insdie their crystals

what temperature would you observe when this is done?

A

increase because its exothermic

123
Q

when heated continuously, pink cobalt chloride cyrstals can be changed into blue crystals

CoCl2 • 6H2O (pink) ⇌ CoCL2 • 2H2O + 4H2O (blue)

the symbol ⇌ tells you that the reaction is reversible

the pink cobalt chloride cyrstals have water trapped inside their crystal structure

blue cobalt chloride crystals have less water trapped insdie their crystals

suggest how the colour changes of these crystals could be used

A

thermometers in a room

124
Q

many fuels ontain sulphur as an impurity

state the gas that forms when sulphur burns in air and describe the environmental effect of this gas in the atmosphere

A

sulphur dioxide is formed

when mixed with air particles an help form acid raid which in turn damages buildings, wildlife and water resources

125
Q

chose the best conditions for the Haber process and explain why they would produce a high yield of ammonia and why they are used in industry

2000atm and 4500oC

200atm and 450oC

20atm and 450C

A

200atm and 450oC

450oC is a compromise of temperature

it is best in this reaction to use an extremely low temperature to increase the yield of product but this is uneconomical as the rate of reaction is too low so you must have a compromise of 450oC

200atm is a relatively high pressure to increase the yield of ammonia but if it is any higher it is too expensive and there is a danger of explosions

ONE MORE MARK CHECK

126
Q

brown nitrogen dioxide, NO2, exists in equilibrium with colourless dinitrogen tetroxide, N2O4

2NO2 (g) ⇌ N2O4(g)

ΔH = -57.2 kJ mol-1

the pressure is increased. when equilibrium is restored, the appearance of the mixture of gases will be:

a) colourless
b) unchanged
c) paler brown
d) darker brown

A

c) paler brown

the reaction moved foward with the increase in pressure

127
Q

brown nitrogen dioxide, NO2, exists in equilibrium with colourless dinitrogen tetroxide, N2O4

2NO2 (g) ⇌ N2O4 (g)

ΔH = -57.2 kJ mol-1

the temperature is increased. when equilibrium is restored, the appearance of the mixture of gases will be:

a) colourless
b) unchanged
c) paler brown
d) darker brown

A

d) darker brown

the reaction moved backwards

CHECK BACKWARDS SHIZ

128
Q

in the catalytic converter of a car engine’s exhauset system, the following reaction occurs:

2NO(g) + 2CO(g) ⇌ N2(g) + 2CO2(g)

ΔH = -745 kJ mol-1

the temperture in a catalytic converter is high

state the effect, if any, on the position of equilibrium if the temperature is lowered

give a reason for your answer

A

effect = increase in exothermic direction

reason = endothermic reactions absorb heat so if the temperature is lowered then temperature needs to be released (exothermic) to restore equilibrium

129
Q

in the catalytic converter of a car engine’s exhauset system, the following reaction occurs:

2NO(g) + 2CO(g) ⇌ N2(g) + 2CO2(g)

ΔH = -745 kJ mol-1

the temperture in a catalytic converter is high

the gases from the engine are not cooled before entering the converter

explain why this is so

A

higher temperature increases the rate of reaction and so it is economical for the system to have a lower temperature

higher temperature = particles on left have activation energy

130
Q

in the catalytic converter of a car engine’s exhauset system, the following reaction occurs:

2NO(g) + 2CO(g) ⇌ N2(g) + 2CO2(g)

ΔH = -745 kJ mol-1

the temperture in a catalytic converter is high

state the effect, if any, of the position of equilibrium if the pressure on the reacting gases is increased

give a reason for your answer

A

effect = increase in product

reason = there are less atoms on the left once pressure in increased so the position of equilibrium shifts to the right to restore equilibrium

131
Q

the reaction of heated magnesium with steam is faster than the reaction of magnesium with cold water. this is mainly because

a) in cold water, the water molecules do not collide as frequently with magnesium
b) the coating of oxide on magnesium decomposed when it is heated
c) the fraction of particles with enegry greater than the activation energy is higher in the recation with steam
d) the recation with steam gos by an alternative route (catalyst) with lower activation energy

A

c) the fraction of particles with enegry greater than the activation energy is higher in the recation with steam

(a and b are also correct but c is more correct)

132
Q

This reaction is used to manufacture ammonia:

N2 + 3H2 ⇌ 2NH3

△H = -x kJ/mol

Bond N≡N has a dissociation energy (kJ/mol) of 944

Bond H-H has a dissociation energy (kJ/mol) of 436

Bond N-H has a dissociation energy (kJ/mol) of 388

calculate the energy change occuring during the reaction to manufacture ammonia

A

944 + (3 x 436) ⇌ 2 x (388 x 3)

2252 ⇌ 2328

2252 - 2328

= - 76

133
Q

to obtain a reasonable yield of ammonia the reaction is carried out at a temperature of 4500C and a pressure of 250 atmospheres

predict what will happen to the yield of ammonia in the equilibrium mixture if the temperature is increased

A

yield will decrease

134
Q

to obtain a reasonable yield of ammonia the reaction is carried out at a temperature of 4500C and a pressure of 250 atmospheres

predict what wil happen to the yield of ammonia in the equilibrium mixture if the temperature is increased

A

yield will decrease

135
Q

the temperature of a mixture of nitrogen, hydrogen and ammonia gases is decreased until all the gases have liquefied

describe two canges in the movement of gas molecules as a gas liquefies

A

molecules will get closer together

molecules will lose kinetic energy (slow down)

136
Q

molecule N2 has a heat of vaporisation (kJ/mol) of 2.8

molecule H2 has a heat of vaporisation (kJ/mol) of 0.45

molecule NH2 has a heat of vaporisation (kJ/mol) of 23

which of these gases will be the last to liquefy?

A

NH3

you have to take the most energy out of the NH3 gas

137
Q

This reaction is used to manufacture ammonia in the Haber process:

N2 + 3H2 ⇌ 2NH3

△ = -92 kJ/mol

a temperature of 4500C and a pressure of 200 atmospheres are often used

if you decrease the temperature what will happen to the rate of reaction and yield of ammonia?

A

rate of reaction will decrease

yield of ammonia will increase

138
Q

This reaction is used to manufacture ammonia in the Haber process:

N2 + 3H2 ⇌ 2NH2

△ = -92 kJ/mol

a temperature of 4500C and a pressure of 200 atmospheres are often used

if you add a catalyst what will happen to the rate of reaction and yield of ammonia?

A

rate of reaction will increase

yield of ammonia will not be affected (no change)

139
Q

state and explain, using the kinetic theory, the effect on the rate of reaction of increasing the concentration of nitrogen in the Haber process

A

increases the number of particles (of nitrogen) in the system

particles collide more frequently

increases proportion of successful collisions because of the higher rate of reaction

140
Q

under the conditions used in the Haber process the yield of ammonia is about 15%

what happens to the unreacted nitrogen and hydrogen?

A

it is reused

141
Q

The equation for the complete combustion of methane is:

CH4 + 2O2 –> CO2 + 2H2O

the bond C-H has a dissociation energy (kJ/mol) of 412

the bond O-H has a dissociation energy (kJ/mol) of 463

the bond O=O has a dissociation energy (kJ/mol) of 496

the bond C=O has a dissociation energy (kJ/mol) of 743

use these values to calculate the energy change occuring during the complete combustion of methane

A

(412 x 4) + (496 x 2) –> (743 x 2) + (463 x 4)

2640 –> 3338

2640 - 3338

  • 698 kJ/mol
142
Q

the biggest error in this experiment is heat loss

suggest how the apparatus could be modified to reduce heat loss

A

put a lid of op

put it in an insulator - e.g. polystyrene or plastic

143
Q

suggest why it is important to stir the chemicals thoroughly

A

so they react and mix and collide with each other

144
Q

which one of these experiments was probably carried out on a different day to the others and why?

A

experiment 2

it has a different room temperature

145
Q

suggest ehy experiment 4 should not be used to calculate the average change

A

its temperature change is anomalous

146
Q

calculate the average temperature change from the first three experiments

A

(7.2 + 7.0 +6.8) ÷ 3

= 7

147
Q

use the following equation to calculate the energy change for this reaction:

energy change in joules = 100 x 4.2 x average temperature change

A

100 x 4.2 x ((7.2 + 7.0 +6.8) ÷ 3)

100 x 4.2 x 7

= 2940 J

148
Q

in the equilibrium below, what effect would an increase in temperature have on the system (rate and yield)?

2H2S + SO2 ⇌ 3S + 2H2O

△H is negative

A

increase in rate

decrease in yield

149
Q

in the equilibrium below, what effect would an decrease in pressure have on the system (rate and yield)?

2H2S + SO2 ⇌ 3S + 2H2O

△H is negative

A

decrease in rate

increase in yield

Chemisty (20 decks)

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