5.1.1 How Fast

Question 1

Define rate of reaction

Answer 1

Change in concentration of a reactant or a product per unit time

Question 2

At a given instant, how could you calculate the rate of a reaction?

Answer 2

Rate of reaction = change in conc of reactants or products / time

Question 3

If the order is zero with respect to a reactant, what does that mean?

Answer 3

Changing the conc of the reactant has no effect on the rate

Question 4

What is the effect on rate in a first order reaction?

Answer 4

Rate is directly proportional to the concentration

Question 5

What is the effect on rate in a second order reaction?

Answer 5

Change in rate = change in conc squared

Question 6

Write a generic rate equation and state what each term means

Answer 6

Rate = k [A]a [B]b

k=rate constant
[A] and [B] are concenrations
a and b are the orders of reaction

Question 7

Do zero order reactants appear on rate equation? Why?

Answer 7

No

because they dont have an effect on the rate

Question 8

How is the overall order of a reaction calculated?

Answer 8

Sum of individual orders

Question 9

How would you calculate the units of the rate constant?

Answer 9

Units of rate are mol dm-3 s-1
units of conc are mol dm-3

Rearrange rate equation to get k =
sub in units and cancel them out

Question 10

When the overall order is 3, what would be the units for rate constant?

Answer 10

dm6 mol-2 s-1

Question 11

How could you measure the rate of reaction experimentally (different methods)

Answer 11

Use a colorimeter at suitable intervals if there is a colour change

If gas is involved, use a gas syringe to collect volume of gas evolved or measure the change in mass of the reaction mixture

Question 12

What does half life mean?

Answer 12

The time taken for concentration of a reactant to decrease by half

Question 13

What is the symbol for half life?

Answer 13

t 1/2

Question 14

What is the relationship between first order reactions and half life?

Answer 14

First order reactants have constant half lifes

Question 15

What is the equation that is used to determine rate constant using half life in a first order reaction?

Answer 15

k = ln2 /t 1/2

Question 16

What is the relationship between rate and time?

Answer 16

Rate proportional 1/t

Question 17

How to determine the rate constant from a rate concentration graph of first order?

Answer 17

k = rate / conc

Question 18

What is rate determining step?

Answer 18

The slowest step in a reaction with multiple steps

Question 19

How does the rate determining step link to the species involved in the rate equation?

Answer 19

Any species involved in the rate determining step appear in the rate equation. Species only involved after the rate determining step do not appear in the rate equation

Question 20

For a reactant in the rate equation, which indicates how many molecules of that reactant ae involved in the rate determinigng step?

Answer 20

The order of the reactant

Question 21

The rate equation of a reaction is rate = k[NO]^2.

How many molecules of NO will be present in the rate dtermining equation

Answer 21

2

Question 22

What affects the vale f the rate constant for a given reaction

Answer 22

Temp only

Question 23

What is the effect of 10 degrees temp increase on the rate roughly?

Answer 23

Doubles rate of reaction

Question 24

What is the Arrhenius equation?

What does each term mean?

Answer 24

k = Ae -Ea/RT

k=rate constant
A= no. collisions between reactant molecules
e
R= gas constant
T= temp in kelvin
Ea = activation energy in joules

Question 25

How can you convert the Arrhenius equation into a useful form for plotting a graph

Answer 25

ln k = -Ea/ RT +lnA

Graph of ln k against 1/T is a straight line
gradient = -Ea/R
y intercept = ln A