10) Reaction rates and equilibrium Flashcards Preview

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Flashcards in 10) Reaction rates and equilibrium Deck (35)
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1
Q

Define rate of reaction

A

the change in concentration of a reactant or product in a given time

2
Q

rate = ?

A

change in conc. / time

3
Q

When is rate fastest?

A

at the start of a reaction as each reactant is at its highest concentration

4
Q

What is rate affected by?

A

conc. (pressure if gaseous)
temperature
use of catalysts
surface area of solid reactants

5
Q

Define collision theory

A

two reacting particles must collide for a reaction to occur, and must be in the correct orientation and have sufficient energy to overcome the activation energy of the reaction

6
Q

How does an increase in concentration affect rate?

A

increases no. of particles in the same volume
particles are closer together and collide more frequently in a given time
there will be more effective collisions and an increase in rate of reaction

7
Q

When gas is compressed into a smaller volume, and pressure is increased what happens to the concentration of gas molecules?

A

increases as the same no. occupy a smaller volume

8
Q

How can the progress of a chemical reaction by followed?

A

monitoring the removal of a reactant or the formation of a product

9
Q

Name two ways rate of reaction can be measured for reactions that produce gases?

A

monitoring volume of gas produced at regular time intervals using gas collection
monitoring the loss of mass of reactants using a balance
either of these measurements are then plotted against time and a tangent drawn for initial rate

10
Q

What apparatus is used for monitoring volume of gas produced at regular time intervals using gas collection?

A
conical flask
delivery tube
trough filled with water
measuring cylinder, filled with water and held upside down in trough with clamp
stop watch
alternative: gas syringe
11
Q

How can you tell the reaction is compete when monitoring the loss of mass of reactants using a balance?

A

no more mass is lost, remains constant

12
Q

Define catalyst

A

a substance that increases the rate of a chemical reaction without being used up in the process

13
Q

What does a catalyst do?

A

provides can alternative route for the reaction with lower activation energy
may react to form an intermediate or provide a surface on which the reaction can occur but is regenerated at the end

14
Q

Describe homogenous catalysts

A

same physical state as reactants and reacts to form an intermediate, which then breaks down to give the product and regenerate the catalyst

15
Q

Describe heterogeneous catalysts

A

different physical states from reactants
usually solids in contact w/ reactants (g/aq) which are adsorbed (weakly bonded) onto their surface where the reaction takes place. after the product molecules leave the surface by desorption

16
Q

Name 4 common catalysts and their uses in industry

A

Fe (s) - Haber process
Pt / Rh (s) - reforming
Ni (s) - hydrogenation of alkenes
V2O5 (s) - contact process (making SO3 for sulfuric acid)

17
Q

Describe catalytic converters

A

have large surface area for heterogeneous catalysts to convert harmful exhaust gases into less harmful ones which can be released into the atmosphere

18
Q

Comment on the use catalysts with regards to sustainability

A

increase the rate of reaction by lowering Ea
reduces temp. and energy requirements
less electricity / finite fossil fuels used
increases profits and less pollutants linked to global warming

19
Q

Give the x and y axis of a Boltzmann distribution

A
x = energy
y = no. of molecules with a given energy
20
Q

Describe a Boltzmann distribution showing temperature

A

at a higher temperature peak is lower and shifted right
greater proportion of molecules can overcome Ea / have energy greater than or equal to Ea
a greater proportion of collisions will lead to a reaction
increases rate of reaction
more frequent collisions as molecules are moving faster also

21
Q

Describe a Boltzmann distribution showing catalyst use

A

Ea with catalyst (left hand side) and without catalyst labelled
a catalyst provides an alt. reaction route w/ a lower Ea
greater proportion of molecules have energy greater than or equal to lower Ea
on collision more molecules will react
increases rate of reaction

22
Q

Define reversible reaction

A

a reaction that takes place in both forward and reverse directions

23
Q

Define dynamic equilibrium

A

the equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and the concentrations do not change

24
Q

Define position of equilibrium

A

the relative quantities of reactants and products, indicating the extent of a reversible reaction at equilibrium

25
Q

Define Le Chatelier’s principle

A

when a system in dynamic equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of the change and to restore equilibrium

26
Q

If there are more products formed, the position of equilibrium has shifted to the _ and If there are more reactants formed, the position of equilibrium has shifted to the _?

A

right-hand side

left-hand side

27
Q

An increase in temp. results in a shift in the _ direction (ΔH is _ ) and a decrease in temp. results in a shift in the _ direction (ΔH is _)?

A

endothermic
positive
exothermic
negative

28
Q

An increase in pressure results in a shift in the direction of the _ and a decrease in pressure results in a shift in the direction of the _?

A

fewer gas molecules

more gas molecules

29
Q

A catalyst doesn’t change _ - its speeds up the rate of forwards and reverse reactions equally?

A

position of equilibrium

30
Q

Define equilibrium constant Kc

A

a measure of the position of equilibrium, the magnitude of an equilibrium constant indicates whether there are more reactants or more products in an equilibrium system

31
Q

Kc = ?

A

[products] / [reactants]
concentrations at equilibrium
^no of molecules

32
Q

What does Kc = 1 indicate?

A

position of equilibrium halfway between reactants and products

33
Q

What does Kc > 1 indicate?

A

position of equilibrium towards products

34
Q

What does Kc < 1 indicate?

A

position of equilibrium towards reactants

35
Q

The larger the value of Kc, the further the equilibrium lies to the _ and the greater the concentration of _?

A

RHS

products to reactants