M5 - Rates of reaction (how fast?)

Question 1

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

Answer 1

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

Question 2

what is the equation for rate?

Answer 2

rate = change in concentration / time

Question 3

What can a graph plotted with lnk on the y axis against 1/T on the x axis tell us in terms of Ea and A?

Answer 3

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

Question 4

What is the logarithmic form of the Arrhenius equation?

Answer 4

lnk = -E(a)/RT + lnA

Question 5

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

Answer 5

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 6

Why does temperature affect the rate constant?

Answer 6

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

Question 7

What is the rate determining step?

Answer 7

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

Question 8

What is a reaction mechanism?

Answer 8

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

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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 11

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

Answer 11

the two ways of monitoring are
Gas collection
Mass loss

Question 12

what is a half life?

Answer 12

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 13

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

Answer 13

Question 14

What is initial rate?

Answer 14

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

Question 15

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

Answer 15

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

Question 16

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

Answer 16

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

Question 17

what is the overall order?

Answer 17

if two reactats A and B with orders m and n

the overall order = m+n

Question 18

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

Answer 18

Reaction rate would quadruple.

Question 19

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

Answer 19

Reaction rate would double.

Question 20

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

Answer 20

Reaction rate would not change.

Question 21

what does second order mean?

Answer 21

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

Question 22

what does first order mean?

Answer 22

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

Question 23

what does zero order mean?

Answer 23

rate ∝ [A]°

rate is NOT affected by concentration

Question 24

What is rate measured in?

Answer 24

Mol dm^-3 s^-1

Question 25

whats the equation for rate?

Answer 25

rate = change in concentration / time

Question 26

What is a reaction’s rate?

Answer 26

The change in concentration per second.

Question 27

What do the rate v concentration graphs of zero, first and second order look like? Explain their shapes

Answer 27

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

Question 28

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

Answer 28

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 29

Why does temperature affect the rate constant?

Answer 29

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

Question 30

What is a reaction mechanism?

Answer 30

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

Question 31

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

Answer 31

k = ln2 / t1/2

Question 32

what does first order mean?

Answer 32

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

Question 33

what does zero order mean?

Answer 33

rate ∝ [A]°

rate is NOT affected by concentration

Question 34

What is the common unit of rate?

Answer 34

Mol dm^-3 s^-1

Question 35

What is the equation for rate?

Answer 35

rate = change in concentration / time

Question 36

Answer 36

A

Question 37

Answer 37

C

Question 38

Answer 38

C

Question 39

Answer 39

A

Question 40

Answer 40

C

Question 41

What is the Half-life of a reactant, t1/2?

Answer 41

Time taken for the concentration of the reactant to reduce by half

Question 42

What is the Rate-determining step? (1)

Answer 42

Is the slowest step of a multi-step reaction (1)