Energy Changes

Question 1

What is an endothermic reaction?

Answer 1

When a reaction takes in more energy from the surroundings during a reaction than it gives out. The reaction ends with more energy than what it started with.

Question 2

What is an exothermic reaction?

Answer 2

When more energy is released into the surroundings than the amount of energy that is gained from the reaction. The reaction ends with less energy than it started.

Question 3

What are some examples of an endothermic reaction?

Answer 3

• An ice pack,
• Thermal decomposition reactions
• reaction between citric acid + sodium hygrogencarbonate.

Question 4

What are some examples of an exothermic reaction?

Answer 4

• Combustion reactions,
• A lot of oxidation reactions,
• Most neutralisation reactions.

Question 5

How can energy be lost in a reaction?

Answer 5

It can dissipate into the surroundings as heat/sound, but mostly heat.

Question 6

How can you test if a reaction is an endo or exothermic reaction?

Answer 6

• Create a reaction and see the change in temperature,
• If the temperature is greater than what it started with then the reaction is endothermic/ if the temperature is less then it is exothermic.
• However, energy is easily lost to the surroundings so measures can be taken to stop the loss of heat:
• Put the polystyrene cup (where your reaction is taking place) into a beaker filled with cotton wool to provide insulation,
• Put a lid onto the beaker to prevent energy lost by evaporation,
• This experiment can also be used to check the effect that other factors have on the energy transferred in a reaction e.g. if a higher concentration of acid means more or less energy is lost or gained.

Question 7

What does the reaction profile for an endothermic reaction look like?

Answer 7

• They have a higher level of energy at the end of the reaction than at the start.
• The activation energy is high.

Question 8

What does the reaction profile for an exothermic reaction look like?

Answer 8

• They have a lower level of energy at the end of the reaction than at the start.
• The activation energy is low.

Question 9

What type of reaction is bond forming?

Answer 9

Exothermic - energy is released as the bond is made.

Question 10

What type of reaction is bond breaking?

Answer 10

Endothermic - energy comes into the molecule to break the bond.

Question 11

Is the reaction endo or exothermic if it takes more energy to make bonds?

Answer 11

Exothermic

Question 12

Is the reaction endo or exothermic if it takes more energy to break bonds?

Answer 12

Endothermic

Question 13

How is electricity produced in a battery?

Answer 13

• Two electrodes are connected with a wire,
• Each electrode is made of a conductive metal on the reactivity series,
• This reacts with an electrolyte, a molten ionic compound to create a charge difference,
• The charge difference creates an electric current in the wire, a voltmeter can be used to measure pd of the battery.

Question 14

What will change the potential difference in a battery?

Answer 14

• If the electrodes are further away from each other in the reactivity series, the potential difference is high,
• If the metals are close to each other on the reactivity series, the pd will not be very high, therefore less electricity is produced,
• The electrolyte will also effect the voltage, some electrolytes work better with specific metals.

Question 15

What is the difference between a cell and a battery?

Answer 15

• A cell is one set of electrodes reacting with an electrolyte,
• A battery is a group of cells connected in series.

Question 16

Why are batteries non-rechargeable?

Answer 16

• All the electrolyte gets used up, an example of a non-rechargeable battery is an alkali battery.
• The reaction is not reversible so the battery must be changed for a new source of electricity.