c6 - rate of reaction

Question 1

How is rate of reaction calculated?

Answer 1

Rate of reaction (mol/s) = Moles of reactant used or product formed / time

Question 2

Name three common ways of measuring rate of reaction

Answer 2

• Loss in mass of reactants
• Volume of gas produced
• Time for a solution to become opaque

Question 3

Describe measuring the rate by monitoring mass
loss

Answer 3

Place the reaction flask on a balance
In these reactions (e.g. metal carbonate + acid) a gas is given off,
so record the decrease in mass in time intervals (note
hydrogen is too light).
Plot a graph of mass vs time

Question 4

Describe measuring the rate by monitoring the volume of a
gas

Answer 4

Connect a gas syringe to a reaction flask and measure the volume of a gas
formed in time intervals. Plot a graph of volume vs time.

Question 5

Describe measuring the rate by monitoring the
disappearance of a cross

Answer 5

Take a piece of paper and mark a cross (X) on it.
Put the reaction flask on this cross.
Mix the reagents, and measure how long it takes for a cloudy mixture to conceal a cross

Question 6

State five factors affecting the
rate of a chemical reaction

Answer 6

• Concentration of reactants
• Pressure of gases (volume)
• Surface area
• Temperature
• Catalysts

Question 7

What is the collision theory?

Answer 7

Chemical reactions can occur only when reacting particles collide with each other with sufficient energy (more than or equal to activation energy)

Question 8

Describe and explain the effect of increasing temperature on the rate of reaction

Answer 8

As T increases, kinetic energy of particles increases, i.e. more energetic collisions
Also, they move faster, so they collide more frequently

Question 9

Describe and explain the effect of increasing
concentration on the rate of reaction

Answer 9

Conc. increases = faster reaction,
More reactants = more frequent collisions

Question 10

Describe and explain the effect
of increasing pressure of a gas
on the rate of reaction

Answer 10

It increases the number of gas molecules in the same volume and
so increases the frequency of collisions and therefore increases the rate of
reaction.

Question 11

what is the relationship between pressure and volume

Answer 11

inversley proportional

Question 12

Describe and explain the effect of increasing surface
area

Answer 12

Increasing the surface area of solid reactants increases the frequency of collisions
and so increases the rate of reaction

Question 13

What is a catalyst?

Answer 13

A catalyst changes the rate of reaction but is not used up

Question 14

what does a catalyst do

Answer 14

It increases rate of
reaction by providing a different pathway for the reaction that has a lower
activation energy.

Question 15

what will the reaction profile look like for a catalyst reaction

Answer 15

a lower
maximum of the curve

Question 16

what is an enzyme

Answer 16

An enzyme is a molecule that acts as a catalyst in a biological system

Question 17

What is a reversible reaction?

Answer 17

A reversible reaction occurs when the products of a reaction can react backwards
to produce the original reactants

Question 18

When is dynamic
equilibrium reached?

Answer 18

In a closed system, when the forward and reverse reactions occur at the same rate
and theconcentrations of reactants and products remain constant.

Question 19

Describe Le Chatelier’s Principle

Answer 19

If a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract change and restore the equilibrium.

Question 20

Describe the effect of
lower the concentration of reactant

Answer 20

equilibrium will shift to the left (reactants)
to make more reactants
and oppose change

Question 21

Describe the effect of
increasing temperature

Answer 21

equilibrium will shift to the left
favouring endothermic
to oppose change

Question 22

Describe the effect of
increasing pressure

Answer 22

equilibrium position to shift towards the side with the smaller number of molecules

Question 23

Describe the effect of a
catalyst on the position of the
equilibrium

Answer 23

No effect.
It just speeds up both forward and backward reactions equally.

Question 24

if you lower the concentration of the products

Answer 24

equilibrium will shift to the left
to make more products
and oppose change

Question 25

if you decrease temp

Answer 25

will shift to the right
favouring exothermic
and oppose change

Question 26

if you decrease pressure

Answer 26

the equilibrium position to shift towards
the side with the larger number of molecules