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Flashcards in Module 5.1 Deck (40)
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1
Q

Define rate of reaction

A

The change in concentration of a reactant or product per unit of time

2
Q

List ways in which we can measure the rate of reaction?

A
Measure the loss in mass
Measure how fast a gas in produced 
Measure how long it takes for a solution to go cloudy
Measure the pH change of a reaction
Watch for colour change
3
Q

When measuring a change in mass, what should you use?

A

A weighting scale

4
Q

When measuring how fast a gas is produced, what should you use?

A

A gas syringe

5
Q

When measuring how long it takes for colour change, what should you use?

A

Colourimetry

6
Q

What is meant by order?

A

With respect to a reactant, the order is the power to which the concentration of a reactant is raised to in the rate equation

7
Q

What 3 orders must we be aware of?

A

Zero order
First order
Second order

8
Q

What does the concentration-time graph of a zero order reactant look like?

A

Straight line downards

9
Q

What does the rate-concentration graph of a zero order reactant look like?

A

Straight line

10
Q

With zero order reactants, what will happen to the rate, if the concentration of the reactant is changed?

A

Nothing

11
Q

With zero order reactants, what pattern does its half-life follow?

A

DECREASES with time

12
Q

What does the concentration-time graph of a first order reactant look like?

A

Slopes downwards

13
Q

What does the rate-concentration graph of a first order reactant look like?

A

Straight line upwards

14
Q

With first order reactants, what will happen to the rate, if the concentration of the reactant is changed?

A

The rate changes by a proportionally equal amount

15
Q

With first order reactants, what pattern does its half-life follow?

A

Constant

16
Q

What does the concentration-time graph of a second order reactant look like?

A

Slopes downwards

17
Q

What does the rate-concentration graph of a second order reactant look like?

A

Slopes upwards (exponential growth)

18
Q

With second order reactants, what will happen to the rate, if the concentration of the reactant is changes by X?

A

The rate will change by X^2

19
Q

With second order reactants, what pattern does its half-life follow?

A

Increases with time

20
Q

Define overall order

A

The sum of the orders of all the different reactants

21
Q

If the overall order of a reaction is 0, what units does the rate constant have?

A

mol dm^-3 s^-1

22
Q

If the overall order of a reaction is 1, what units does the rate constant have?

A

s^-1

23
Q

If the overall order of a reaction is 3, what units does the rate constant have?

A

dm^3 mol ^-1 s^-1

24
Q

If the overall order of a reaction is 4, what units does the rate constant have?

A

dm^6 mol ^ -2 s^-1

25
Q

What is meant by the rate constant?

A

The constant that links the rate of reaction with the concentration of the reactants raised to the powers of their orders in a rate equation

26
Q

What form do rate equations take?

A

r = k[A]^m x [B]^n

Where A is the concentration of reactant A
Where B is the concentration of reactant B
Where m is the order of reactant A
Where n is the order of reactant B

27
Q

Define the term half-life

A

The time taken for HALF of the reactant to be used up

28
Q

What is the half-life pattern for zero order reactants?

A

Decreases with time

29
Q

What is the half-life pattern for first order reactants?

A

Remains constant throughout the reaction

30
Q

What is the half-life pattern for second order reactants?

A

Increases with time

31
Q

Define the term, the rate determining step

A

The slowest step in the reaction mechanism of a multi-step reaction

32
Q

Are chemicals in the rate equation in the rate determining step?

A

Yes

33
Q

In the rate equation, if a chemical is second order, how many moles of it will be in the rate determining step?

A

2 moles

34
Q

If identical chemicals appear on the same side of the reaction mechanism steps, what do we do?

A

ADD them together

35
Q

If identical chemicals appear on opposite side of the reaction mechanism steps, what do we do?

A

Subtract them

36
Q

Give the overall equation for this reaction

Step 1) 2N2O5 → N2O4 + 2NO3
Step 2) N2O4 + NO3 → NO + O2 + 2NO2
Step 3) NO + NO3 → 2NO2

A

2N2O5 → 4NO2 + O2

37
Q

What equation to find k, can only be used when the overall order is 1?

A

k = ln(2) / Half-life (seconds)

38
Q

What are the units for half-life?

A

Seconds (unless stated otherwise)

39
Q

Why does the equation k = ln(2) / Half-life only work when the overall order is 1?

A

First order reactants have a constant half-;life

40
Q

How can we investigate reaction rates using the initial rates method?

A

Step 1) Carry out the reaction, continuously measuring one reactant
Step 2) Use this to draw a concentration-time graph
Step 3) REPEAT the experiment using a different initial concentration
Step 4) REPEAT the process for each reactant at regular time intervals and find the rates and orders