Calculating and explaining energy change

Question 1

What is the unit of measurement for energy?

Answer 1

The joule, J.

Question 2

How much energy does it take to heat up 1g of water by 1^oC?

Answer 2

4.2 joules of energy.

Question 3

How many joules is 1 calorie?

Answer 3

4.2 joules.

Question 4

What is information about the energy provided by food products given in?

Answer 4

Kilocalories (kcal).

Question 5

What is a chemical change always accompanied by?

Answer 5

An energy change.

Question 6

What can calorimetry be used to measure?

Answer 6

The relative amounts of energy produced by food or fuels.

Question 7

What method is used to measure the temperature change that takes place when a fuel burns?

Answer 7

1. Place 100g of water in a calorimeter.
2. Measure the temperature of the water.
3. Find the mass in grams of the fuel to be burned.
4. Burn the fuel under the water in the calorimeter for a few minutes.
5. Record the new temperature of the water.
6. Calculate the temperature change.
7. Weigh the fuel.
8. Calculate how much fuel has been used.
9. Calculate the energy released.

Question 8

What formula can be used to calculate the energy released by a fuel?

Answer 8

Q = mcΔT
where:
Q is the energy released in J
m is the mass of water being heated,
c is 4.2
ΔT is the temperature change.

Question 9

What happens in a chemical reaction?

Answer 9

New substances are produced.

Question 10

What must happen for new substances to be produced in a chemical reaction?

Answer 10

The bonds in the reactants must be broken and new bonds are made to form the products.

Question 11

What does breaking a chemical bond require?

Answer 11

Lots of energy.

Question 12

What happens once a new chemical bond has been formed?

Answer 12

Energy is given out.

Question 13

When is a reaction exothermic?

Answer 13

The energy released from forming new bonds is greater than the energy needed to break existing bonds. Energy is transferred to the surroundings.

Question 14

When is a reaction endothermic?

Answer 14

The energy needed to break existing bonds is greater than the energy released from forming new bonds. Energy is absorbed from the surroundings.

Question 15

How can the amount of energy produced in a chemical reaction in solution be measured?

Answer 15

By mixing the reactants in an insulated container so that the temperature change is measured before heat is lost to the surroundings.

Question 16

What reactions would measuring the energy produced in a chemical reaction in solution by mixing reactants in an insulated container be suitable for?

Answer 16

Neutralisation reactions and reactions involving solids.

Question 17

How can the energy transferred in a reaction be calculated?

Answer 17

1. Work out the energy used to break the bonds in the reaction.
2. Work out the energy given out by making bonds.
3. Work out the energy change; step 1 - step 2.
4. If the energy change is positive, it is endothermic.
5. If the energy change is negative, it is exothermic.

Question 18

What is the activation energy?

Answer 18

The energy needed to start a reaction.

Question 19

What do catalysts do in a reaction?

Answer 19

they reduce the activation energy needed for a reaction, making the reaction go faster.

Question 20

What are two uses of hydrogen?

Answer 20

1. As a fuel in combustion engines.

2. In fuel cells, which produce electricity that can be used to power vehicles.

Question 21

What is the word equation for the combustion of hydrogen?

Answer 21

hydrogen + oxygen -> water (+ heat)