5.1 - Rates, Equilibrium and pH

Question 2

Define rate of reaction

Answer 2

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

Question 3

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

Answer 3

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

Question 4

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

Answer 4

A weighting scale

Question 5

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

Answer 5

A gas syringe

Question 6

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

Answer 6

Colourimetry

Question 7

What is meant by order?

Answer 7

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

Question 8

What 3 orders must we be aware of?

Answer 8

Zero order First order Second order

Question 9

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

Answer 9

Straight line downards

Question 10

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

Answer 10

Straight line

Question 11

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

Answer 11

Nothing

Question 12

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

Answer 12

DECREASES with time

Question 13

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

Answer 13

Slopes downwards

Question 14

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

Answer 14

Straight line upwards

Question 15

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

Answer 15

The rate changes by a proportionally equal amount

Question 16

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

Answer 16

Constant

Question 17

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

Answer 17

Slopes downwards

Question 18

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

Answer 18

Slopes upwards (exponential growth)

Question 19

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

Answer 19

The rate will change by X^2

Question 20

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

Answer 20

Increases with time

Question 21

Define overall order

Answer 21

The sum of the orders of all the different reactants

Question 22

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

Answer 22

mol dm^-3 s^-1

Question 23

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

Answer 23

s^-1

Question 24

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

Answer 24

dm^3 mol ^-1 s^-1

Question 25

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

Answer 25

dm^6 mol ^ -2 s^-1

Question 26

What is meant by the rate constant?

Answer 26

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

Question 27

What form do rate equations take?

Answer 27

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

Question 28

Define the term half-life

Answer 28

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

Question 29

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

Answer 29

Decreases with time

Question 30

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

Answer 30

Remains constant throughout the reaction

Question 31

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

Answer 31

Increases with time

Question 32

Define the term, the rate determining step

Answer 32

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

Question 33

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

Answer 33

Yes

Question 34

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

Answer 34

2 moles

Question 35

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

Answer 35

ADD them together

Question 36

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

Answer 36

Subtract them

Question 37

Give the overall equation for this reaction Step 1) 2N2O5 → N2O4 + 2NO3 Step 2) N2O4 + NO3 → NO + O2 + 2NO2 Step 3) NO + NO3 → 2NO2

Answer 37

2N2O5 → 4NO2 + O2

Question 38

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

Answer 38

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

Question 39

What are the units for half-life?

Answer 39

Seconds (unless stated otherwise)

Question 40

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

Answer 40

First order reactants have a constant half-;life

Question 41

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

Answer 41

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