Chapter 18 - Rates of Reactions

Question 1

What is a reaction’s rate?

Answer 1

The change in concentration per second.

Question 2

whats the equation for rate?

Answer 2

rate = change in concentration / time

Question 3

What is rate measured in?

Answer 3

Mol dm^-3 s^-1

Question 4

what does zero order mean?

Answer 4

rate ∝ [A]°

rate is NOT affected by concentration

Question 5

what does first order mean?

Answer 5

rate ∝ [A]¹
rate changes by the same factor as concentration
so if concentration doubles as does rate

Question 6

what does second order mean?

Answer 6

rate ∝ [A]²
rate changes by the factor concentration does squared
if [A] doubles rate quadruples

Question 7

In a chemical reaction, if A is zero order, what effect would be seen if [A] is doubled?

Answer 7

Reaction rate would not change.

Question 8

In a chemical reaction, if A is first order, what effect would be seen if [A] is doubled?

Answer 8

Reaction rate would double.

Question 9

In a chemical reaction, if A is second order, what effect would be seen if [A] is doubled?

Answer 9

Reaction rate would quadruple.

Question 10

what is the overall order?

Answer 10

if two reactats A and B with orders m and n

the overall order = m+n

Question 11

How is the reaction rate at a specific time worked out using a concentration against time graph?

Answer 11

At the set time, draw a tangent to the curve and measure the gradient to get the rate.

Question 12

If there are two reactants, A and B, what would be the rate equation?

Answer 12

rate = k x [A]^m x [B]^n
k - rate constant
m - order of A
n - order of B

Question 13

What is initial rate?

Answer 13

The instantaneous rate at the beginning of an experiment when t=0.

Question 14

what does a zero order and first order concentration time graphs look like?

Answer 14

Question 15

what is a half life?

Answer 15

a half life of a reactant is the time take for its concentration to decrease by half.

a first order reaction has a constant half life

Question 16

What are the two ways of continuous monitoring when a gas is produced?

Answer 16

the two ways of monitoring are
Gas collection
Mass loss

Question 17

What is a way of utilising light to monitor rate?

Answer 17

Using a colourimeter.

Measuring the amount of light absorbed by a solution.

Question 18

What is half life?

Answer 18

The time taken for half of a reactant to be used up.

Question 19

In a concentration time graph, how can you deduce whether the reactant is first or second order?

Answer 19

Measure multiple half lives.
If the half life is constant, it is first order.
If the half life is increasing, it is second order.

Question 20

If the rate is only affected by one reactant, which is first order, what is another way of determining the rate constant?

Answer 20

k = ln|2| / t(1/2)

Question 21

What is a reaction mechanism?

Answer 21

A series of steps that, together, make up the overall reaction.

Question 22

What is the rate determining step?

Answer 22

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

Question 23

Why does temperature affect the rate constant?

Answer 23

Increasing the temperature, increases rate of reaction and thus rate constant.

Question 24

the Arrhenius equation is found on the data sheet what do the symbols stand for?
k = A x e^(-E(a)/RT)

Answer 24

k = A x e^(-E(a)/RT)
A - pre exponential factor
-E(a)/RT - exponential factor 
R=gas constant= 8.314
T= temp in kelvin 
ea=activation energy

Question 25

What is the logarithmic form of the Arrhenius equation?

Answer 25

ln|k| = -E(a)/RT + ln|A|

Question 26

What can the log form of the Arrhenius equation be modelled as?

Answer 26

A straight line graph in y=mx + c
ln|k|=-E(a)/R 1/T +ln|A|
Y= m X + c

ln[A] is the y intercept and -E(a)/RT ia the gradient

Question 27

whats the equation for rate?

Answer 27

rate = change in concentration / time

Question 28

what does the rate concentration graphs of zero, first and second order look like? explain there shapes

Answer 28

zero order
rate∝ [A]^0 therefore rate= constant

first order
rate∝[A]¹ so a linear shape upwards

second order
rate∝[A]² so curve upwards