Rates of Reaction and Energy Changes

Question 1

What is the equation for rate of reaction?

Answer 1

Amount of reaction used/product formed / time

Question 2

What units could be used for rate of reaction?

Answer 2

g/s, cm^3/s and 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 and 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 crossss 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

How does 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

What 2 things could happen when the rate of reaction increases?

Answer 9

More frequent collisions and energy of collisions increases

Question 10

How can the rate of a reaction be increased?

Answer 10

Increase temperature, concentration, surface area to volume ratio, pressure and add a catalyst

Question 11

How does temperature affect the rate of reaction?

Answer 11

The reactants have more energy so more particles have 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

greater surface area means there are more exposed particles so more frequent successful collisions

Question 13

How does catalyst affect the rate of reaction?

Answer 13

It provides an alternative reaction pathway with a lower activation energy so 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

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

There are more reacting particles in the same volume of gas so more frequent successful collisions occur

Question 16

How can you find the rate of reaction using a graph?

Answer 16

X axis: time and Y axis: amount of reactant used/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 17

What is the shape of the curve if a graph is plotted to show time and the amount of gas given off during a reaction?

Answer 17

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

Question 18

What is a catalyst?

Answer 18

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

Question 19

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

Answer 19

It provides an alternate reaction pathway with a lower activation energy

Question 20

What are enzymes?

Answer 20

Act as biological catalysts that increase the rate of reactions in living cells

Question 21

Which enzyme is used to produce ethanol from glucose?

Answer 21

Yeast

Question 22

What does exothermic mean?

Answer 22

A reaction that gives out energy to the surroundings

Question 23

What does endothermic mean?

Answer 23

A reaction that takes in heat energy from the surroundings

Question 24

Are neutralisation reactions endothermic or exothermic?

Answer 24

Exothermic

Question 25

Are displacement reactions endothermic or exothermic?

Answer 25

Either exothermic or endothermic

Question 26

Is a salt dissolving in water endothermic or exothermic?

Answer 26

Either exothermic or endothermic

Question 27

Are precipitation reactions endothermic or exothermic?

Answer 27

Exothermic

Question 28

How could you measure the temperature change of a neutralisation reaction?

Answer 28

Measure initial temperature of the solution, mix both reactants in a polystyrene cup, record the highest temperature reached and calculate the temperature change

Question 29

How could heat loss be minimised during an experiment?

Answer 29

Use polystyrene cup, place reaction cup in a beaker full with cotton wool for extra insulation and lid on the reaction cup

Question 30

What are exothermic and endothermic reactions in terms of bond breaking/forming?

Answer 30

Exothermic: energy released from breaking bonds is greater than the energy used to make bonds
Endothermic: energy released in forming new bonds is greater than the energy used to break old bonds

Question 31

What types of reaction are exothermic?

Answer 31

Combustion and neutralisation

Question 32

What is an example of an endothermic reaction?

Answer 32

Thermal decomposition and photosynthesis

Question 33

How can the energy change of a reaction be calculated from bond energies?

Answer 33

Total energy of bonds broken - total energy of bonds made

Question 34

If the energy change of a reaction is negative, is the reaction exothermic or endothermic?

Answer 34

Exothermic, energy has been lost to the surroundings

Question 35

What is a reaction profile?

Answer 35

A graph showing showing the relative energies of reactant and products a well as the activation energy of a reaction