5.1.1 How Fast?

Question 1

Rate of reaction definition

Answer 1

Change in concentration of a substance in unit time

Unit: mol dm^-3s^-1

Question 2

On a concentration time graph what does the gradient represent

Answer 2

Rate of reaction

Question 3

How do you calculate rate from a graph

Answer 3

Draw a tangent

Question 4

What is the rate constant

Answer 4

K

Question 5

How do you work out the total order of a reaction

Answer 5

Add all the individual orders

Question 6

What do square brackets mean in a rate equation

Answer 6

Concentration

Question 7

Zero order

Answer 7

Concentration has no effect on rate of reaction

Rate= k

Question 8

First order

Answer 8

Rate of reactiln directly proprotional to concentration of A

rate= k[A]

Question 9

Second order

Answer 9

Rate of reaction is proportional to concentration of A squared
rate= k[A]^2

Question 10

Rate concentration for zero order

Answer 10

Line is horizontal
Parallel to the x axis
Rate on y, conc on x axis

Question 11

Rate concentration for first order

Answer 11

Straight line y=x
/ shape
Rate on y, conc on x axis

Question 12

Rate concentration second order

Answer 12

Curved, starts at x and increases exponentially

Rate on y, conc on x axis

Question 13

What is continuous rate data

Answer 13

Data from one experiment where concentration of a substance is followed throughout the experiment

Question 14

How is continuous rate data processed

Answer 14

Plotting data

Calculating successive half lives

Question 15

How to tell if a reaction is first or second order from a graph

Answer 15

Half lives are constant when first order

Question 16

Rate constant k

Answer 16

Units of k depend on overall order of the reaction
Work it out from rate equation
K is independent of concentration and time
Only changes with temperature

Question 17

Calculating a value of k using intial rate data

Answer 17

Use one of the experiments and put the values for each concentration into your calculated equation
Rearrange to find k

Question 18

Effect of temperature on rate constant

Answer 18

Increasing temperature increases rate constant

Relationship is given by arrhenius equation

Question 19

Arrhenius equation to find k

Answer 19

k=Ae^-Ea/RT

Question 20

Rearranged arrhenius

Answer 20

lnk = constant - Ea/RT
plot graph ln rate or lnk on y axis
Then 1/T on x axis
Ea = gradient of line x R

Question 21

Concentration time graph zero order

Answer 21

\
conc on y
Time on x

Question 22

Concentration time graph 1st order

Answer 22

\ but curved slightly
conc on y
Time on x

Question 23

Concentration time graph 2nd order

Answer 23

\ quite curved
conc on y
time on x

Question 24

Arrhenius equation units

Answer 24

Ea= kJ/mol
R= kJ/mol/ K
T= K

Question 25

How to measure rates of reaction

Answer 25

Measure change in volume of gas Measure change in mass Titrating samples of reaction mixture with acid, alkali, sodium thiosulfate Colorimetry Measure change in electrical conductivity Measure of optical activity

Question 26

Measure change in volume of gas

Answer 26

Works if theres a change in number of moles of gas in the reaction Gas syringe

Question 27

Measure change of mass

Answer 27

Works if there’s a gas produced which is allowed to escape | Works better with heavy gases such as CO2

Question 28

Titrating samples of reaction mixture with acid, alkali, sodium thiosulfate

Answer 28

1. Small samples removed from reaction mixture 2. Quench which stops reaction (dilute with water, cooling, add a reagent with one of the reactants) 3. Titrate with a suitable reagent

Question 29

Colorimetry

Answer 29

If one of the reactants or products is coloured then colorimetry can be used to measure the change in colour of the reacting mixtures

Question 30

Measuring change in electrical conductivity

Answer 30

Can be used if theres a change in the number of ions in reaction mixture

Question 31

Measure optical activity

Answer 31

If theres a change in the optical activity through the reaction this could be followed in a polarimeter

Question 32

Slowest step in the reaction

Answer 32

Rate determining step

Question 33

Which step controls the rate of reaction

Answer 33

Rate determining step

Question 34

Number of moles of each substance of molecules in slowest step is the same as what

Answer 34

The order of reaction for each substance | 0 moles of A in slow step means A is zero order