How Fast?

Question 1

What is reaction rate?

Answer 1

The reaction rate is the change in the amount of reactants or products per unit time (normally per second). The unit is mol dm-3 s-1.

Question 2

Briefly, what is the effect of concentration on rate of reaction?

Answer 2

By increasing the concentration, collisions between molecules become more frequent as atoms are closer together which increases the rate of reaction.

Question 3

In a concentration-time graph, how do you find the rate of change of concentration?

Answer 3

It is found from the slope or gradient of the curve/line. You use a tangent for a curve to find the rate of change at a particular point. You can find the rate by Y/X.

Question 4

What does zero order tell you?

Answer 4

If you double the concentration of the reactant, the rate stays the same, the order with respect to that reactant is 0.

Question 5

What does first order tell you?

Answer 5

When the reactant’s concentration doubles and the rate doubles, the order with respect to the reactant is 1.

Question 6

What does second order tell you?

Answer 6

If the reactant’s concentration doubles, the rate quadruples, the order with respect to that reactant is 2.

Question 7

CONCENTRATION V. TIME GRAPHS

What does a zero order graph look like?

Answer 7

A straight line with a constant slope.

Question 8

CONCENTRATION V. TIME GRAPHS

What does a first order graph look like?

Answer 8

A downwardly sloping curve with a constant half life.

Question 9

CONCENTRATION V. TIME GRAPHS

What does a second order graph look like?

Answer 9

A steeper downwardly sloping curve; levels out quicker.

Question 10

RATE OF REACTION V. CONCENTRATION

What does the graph for zero order look like?

Answer 10

A straight line horizontal to the x axis rate is independant of concentration.

Question 11

RATE OF REACTION V. CONCENTRATION

What does the graph for first order look like?

Answer 11

A straight line with a constant slope rate is proportional to concentration.

Question 12

RATE OF REACTION V. CONCENTRATION

What does the graph for second order look like?

Answer 12

An upwardly sloping curve; plotting rate v conc^2 gives a straight line.

Question 13

What is the ‘half-life’?

Answer 13

The time taken for the concentration of a reactant to drop half of its original value.

Question 14

How do you distinguish between the different order reactions?

Answer 14

• First order: half life remains constant.
• Zero order: half-life remains significant decrease this.
• Second order: half-life remains significant increase

Question 15

What the experiment equation?

Answer 15

A + 2B + X —► C + D

Question 16

What is the rate equation?

Answer 16

r = k [A]^x [B]^x

Question 17

What happens to the rate constant if you increase temperature?

Answer 17

You increase the value of the rate constant.

Question 18

What happens to the rate of reaction if you increase the K value?

Answer 18

It increases.

Question 19

What is the slowest step of a reaction called?

Answer 19

The rate determining step.

Question 20

If a reactant appears in the rate equation, it must affect what?

Answer 20

The rate (present in the rate determing step).

Question 21

If a reactant does not appear in the rate equation, it will not affect what?

Answer 21

The rate (not present in rermining step).

Question 22

How do you find the gradient of a curved line?

Answer 22

ΔY

ΔX

Question 23

How do you work out the intiial rate of reaction (in a conc-time graph)?

Answer 23

You calculate the gradient of the tangent at time=0

Question 24

According to the rate equation, what does reaction rate only depend on?

Answer 24

The rate constant and reactant concentration