rate equations

Question 1

Define rate of reaction

Answer 1

The change in concentration per unit of time mol dm-3 s-1

Question 2

Define activation energy

Answer 2

The minimum energy for the reaction to occur

Question 3

Why does a higher temperature increase the rate of reaction

Answer 3

More particles have at least Ea
More frequent successful collisions

Question 4

Why does a higher concentration/pressure increase the rate of reaction

Answer 4

More frequent successful collisions
More particles in given volume

Question 5

Why does breaking a solid into smaller particles increase the rate

Answer 5

Increased surface area
More frequent successful collisions

Question 6

What is the rate

Answer 6

Rate = k / [A] [B]

Question 7

The majority of chemical reactions start off with a fast rate of reaction and then slow down before the reaction stops. This is because :

Answer 7

Initially there is a high concentration of reactants so a large frequencies of successful collisions
As the rate reactants start to get used up successful collisions become less frequent
Once one or more reactants reused up there are zero success collisions

Question 8

What does 0 order mean

Answer 8

Changing [reactants] has no effect on the rate of reaction

Question 9

What does 1st order mean

Answer 9

Change in rate is directly proportional to change in [reactants]

Question 10

What does 2nd order

Answer 10

Change in rate is proportional to the change in [reactants] 2

Question 11

What is the order of reaction for the following
Rate = K[Y]2

Answer 11

2nd order with respect to y
Overall order =2

Question 12

How do you work out the units for rates reaction

Answer 12

Moldm-3 for every letter and in the top with s-1
Cancel them out
Add the ones necessary together

Question 13

What are the 2 types of reaction that determine orders of reactions

Answer 13

Continuous monitoring
Monitoring using physical property

Question 14

How do you work out the results from continuous monitoring

Answer 14

Do the change in y/change in x

Question 15

Define the terms order of reaction and rate constant

Answer 15

?

Question 16

Initial rates

Answer 16

?

Question 17

Iodine clock rates practical

Answer 17

Indicative Chemistry content Method 1
Stage 1 Preparation

1amMeasure (suitable/known volumes of) some reagents (ignore quoted values for volume)
1b Measure (known amount of) X / use a colorimeter
1c into separate container(s) - (allow up to two reagents and X measured together into one container); reference to A, B or C added last. NOT if X added last.

Stage 2 Procedure
2a Start clock/timer at the point of mixing (don’t allow if only 2 reagents mixed)
(allow even if X not added or added last)
26 Time recorded for appearance of blue colour/specific reading on colorimeter/disappearing cross
2c Use of same concentration of B and C / same total volume / same volume/amount of X
2d Same temperature/use water bath
2e Repeat with different concentrations of A (can be implied through different volumes of A and same total volume)

Stage 3 Use of Results
За 1/time taken is a measure of the rate
3b plot of 1/time against volumes/concentrations of A or plot log(1/time) vs
log(volume or concentration of A)
3с description of interpreting order from shape of 1/time vs volume or concentration graph / gradient of log plot gives order / allow interpretation of time vs concentration graph / ratio between change in concentration and change in rate (Qua, 2X[A] = 2 × rate so 1st order)

Question 18

What is the Arrhenius equation, what can it be rearranged to and what do the letters stand for

Answer 18

K = Ae ^ -Ea/ RT
rearranged to
LnK = LnA - Ea/RT

K = rate constant
A = Arrhenius constant
Ea = activation energy
R = Molar gas constant
T = temperature in Kelvin