Rate and Extent of Chemical Change

Question 1

How can you measure the speed of a reaction?

Answer 1

• Recording the amount of product formed

- By recording the amount of reactant used up over time

Question 2

How does a graph represent the rate of a reaction?

Answer 2

steeper gradient - a faster rate of reaction
Over overtime the line becomes less steep - the reactants are used up
Flat lines - the reaction has finished

Question 3

Define the Collision Theory

Answer 3

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

Question 4

Define activation energy

Answer 4

The minimum amount of energy that particles need to react. Particles need this much energy to break the bonds in the reactants and start the reaction.

Question 5

What factors affect the rate of reaction?

Answer 5

• Temperature
• Concentration (liquid)
• pressure (gas)
• Surface area :volume ratio
• catalyst

Question 6

Explain how increasing the temperature, affects the rate of reaction, in terms of energy and collisions

Answer 6

• When the temperature is increased, the particles have more kinetic energy, so they move faster
• there are more frequent collisions between the particles
• More frequent collisions = faster rate of reaction

Question 7

Explain how increasing the concentration/pressure, affects the rate of reaction, in terms of energy and collisions

Answer 7

If a solution is more concentrated, it means there are more particles in the same volume of the solvent.
When the pressure of a gas increases, it means that the same number of gas particles occupies a smaller volume. Therefore the collisions between the reactant particles are more frequent.

Question 8

Explain how increasing the surface area, affects the rate of reaction, in terms of energy and collisions

Answer 8

if one of the reactants is a solid, then breaking it up into smaller pieces will increase the surface area: volume ratio. So, there will be more frequent collisions.

Question 9

Equation for the Rate of Reaction

Answer 9

Rate of reaction = Quantity of reactant used or product formed/ Time

Question 10

3 ways of measuring the rate of reaction

Answer 10

• Disappearing cross/ colour change
• Change in mass
• The volume of a gas given off

Question 11

Mg and HCL practical on the effect of concentration on the rate of reaction

Answer 11

• Add a set volume of HCL acid to a conical flask and place on a mass balance
• Add some Mg ribbon to the acid and quickly plug the flask with cotton wool
• start the stopwatch and record the mass on the balance
• Take readings of the mass at regular intervals
• Repeat with more concentrated acid solutions

Question 12

what is the reason for putting cotton wool at the top of the flask?

Answer 12

it allows the gas to escape but stops the acid from spitting out.

Question 13

What are the control variables of the Mg and HCL practical?

Answer 13

• amount of Mg ribbon

- volume of acid

Question 14

Sodium Thiosulphate and HCL practical on the effect of concentration on the rate of reaction

Answer 14

• Add a set volume of dilute sodium thiosulphate to a conical flask
• place the flask on a piece of paper with a black cross drawn on it
• Add some dilute HCL acid to the flask and start the stopwatch
• Time how long it takes for the black cross to disappear, through cloudy sulphur
• Repeat with different concentrations of ONE reactant at a time
• The reaction produces sulphur dioxide , so the experiment should be carried out in a well ventilated place.

Question 15

What is kept the same in the Sodium thiosulphate practical?

Answer 15

the depth of the liquid

Question 16

What is a reversible reaction?

Answer 16

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