Rate of Reactions

Question 1

What is the equation for rate of reaction?

Answer 1

Rate of reaction =
Amount of reactant used or product formed/
Time (s)

Question 2

What units could be used for rate of reaction?

Answer 2

g/s
cm^3/s
mol/s

Question 3

How can you measure the rate of reaction when a

gas is given off?

Answer 3

• Measure time and collect gas in an upside down
  measuring cylinder in a trough of water or in a gas
  syringe to measure the volume of gas produced.
• Measure time and the change in mass.

Question 4

How can you measure the rate of reaction when a

precipitate is formed?

Answer 4

Put a black cross below a beaker
containing one reactant. Time how long it
takes for the cross to disappear after the
second reactant is added.

Question 5

Why is using the precipitation method to investigate

rate of a reaction not very accurate?

Answer 5

It’s subjective so people are likely to
disagree over the exact point at which
the cross is no longer visible.

Question 6

How can you measure rate of reaction using a digital

balance?

Answer 6

When a gas is produced as this will cause mass
to decrease. The experiment can be carried out
on a digital balance and the rate of reaction can
be calculated by recording the mass at regular
time intervals.

Question 7

What does the term ‘activation energy’ mean?

Answer 7

The minimum amount of energy required
for a reaction to occur between two
reacting particles

Question 8

What must happen for a reaction to occur?

Answer 8

Particles must collide at the correct

orientation with sufficient energy to react.

Question 9

In terms of particles, what 2 things could happen

when the rate of reaction increases?

Answer 9

• More frequent collisions.

- Energy of collisions increases.

Question 10

How can the rate of a reaction be increased?

Answer 10

• Increase the temperature.
• Increase the concentration.
• Increase surface area to volume ratio.
• Add a catalyst.
• Increase the pressure (for gases).

Question 11

How does temperature affect the rate of reaction?

Answer 11

Increasing temperature increases the rate of
reaction. This is because the reactants have more
energy so more particles have energy above the
activation energy meaning more collisions will be
successful. Collisions also occur more frequently
because the particles have more kinetic energy.

Question 12

How does surface area affect the rate of reaction?

Answer 12

Increasing the surface area of reactants
increases the rate of reaction. This is
because a greater surface area means
there are more exposed particles so
more frequent successful collisions.

Question 13

How does a catalyst affect the rate of reaction?

Answer 13

A catalyst increases the rate of reaction. This is
because it provides an alternate reaction
pathway with a lower activation energy. More
particles will have sufficient energy to overcome
the activation energy and react so more
successful collisions occur in the same time

Question 14

How does concentration affect the rate of reaction?

Answer 14

Increasing concentration increases the rate
of reaction. This is because there are more
reacting particles in the same volume so
there are more frequent successful
collisions.

Question 15

How does pressure affect the rate of a gaseous

reaction?

Answer 15

Increasing the pressure of a gaseous reaction
increases the rate of reaction. This is because there
are more reacting particles in the same volume of
gas (or the same number of particles in a smaller
volume) so more frequent successful collisions
occur

Question 16

Marble chips react with hydrochloric acid to produce
calcium chloride, water and carbon dioxide. How
could you measure the rate of reaction?

Answer 16

Since gaseous carbon dioxide is released,
the rate can be measured by using a digital
balance to measure the change in mass
over a period of time.

Question 17

Marble chips react with hydrochloric acid to produce
calcium chloride, water and carbon dioxide. How
could the rate of this reaction be increased?

Answer 17

• Increase the surface area of the marble
  chips by turning them into a powder.
• Increase concentration of acid.
• Increase temperature.

Question 18

After completing an experiment, how can
you find the rate of reaction using a
graph?

Answer 18

Plot:
● X axis: time
● Y axis: amount of reactant used or product formed

Draw a tangent to a point on the graph and find the
gradient of this line to find the rate of reaction at that
time.

Question 19

A graph showing time and the amount of gas given
off during an experiment has a steep gradient. What
does this tell you about the rate of the reaction?

Answer 19

Fast rate of reaction.

Question 20

A graph is plotted to show time and the amount of gas given off during a reaction.

Describe the shape of the curve

Answer 20

Initially the curve is very steep as the rate of reaction is relatively fast at
the start.
The curve becomes less steep as the reactants get used up because
there are fewer successful collisions occurring.
At the end, the graph is a flat line because all the reactants have been
turned into products.

Question 21

What is a catalyst?

Answer 21

A substance which speeds up the rate of
a reaction without being chemically
changed at the end.

Question 22

How does a catalyst speed up the rate of a reaction?

Answer 22

It provides an alternate reaction pathway

with a lower activation energy.

Question 23

What are enzymes?

Answer 23

Enzymes act as biological catalysts that
increase the rate of reactions in living
cells.

Question 24

Which enzyme is used to produce ethanol from

glucose?

Answer 24

Yeast