Energy Change

Question 1

What is an exothermic reaction?

Answer 1

A reaction that gives out energy to its surroundings

Question 2

What is an endothermic reaction?

Answer 2

A reaction that takes in energy from its surroundings.

Question 3

Is bond breaking endothermic or exothermic?

Answer 3

Endothermic

Question 4

Is bind forming endothermic or exothermic?

Answer 4

Exothermic

Question 5

Describe the energy change in an exothermic reaction.

Answer 5

The energy released on bond formation is greater than the energy used in breaking existing bonds. The left over energy is released into the surroundings.

Question 6

Describe the energy change in an endothermic reaction.

Answer 6

The energy required to break the existing bonds is greater than the energy released when the new bonds are formed. The extra energy needed is absorbed from the surroundings.

Question 7

What is bond enthalpy?

Answer 7

The amount of energy required to make or break a specific bond.

Question 8

How do you work out the overall energy change in a reaction?

Answer 8

Energy change= energy of bond breaking - energy of bond making

Question 9

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

Answer 9

Exothermic

Question 10

If the overall energy change is positive, is the reaction exothermic or endothermic?

Answer 10

Endothermic

Question 11

What is an energy level diagram?

Answer 11

A graph that shows how the energy in a reaction changes as the reaction progresses.

Question 12

How is overall energy change showed on an energy level diagram?

Answer 12

The distance between the reactants line and the products line

Question 13

What does the energy level diagram for an exothermic reaction look like?

Answer 13

The teactants have more energy than the products so there’s a smooth curve down.

Question 14

What does the energy level diagram for an endothermic reaction look like?

Answer 14

The products have more energy than the reactants so there’s a smooth curve up.

Question 15

How is activation energy shown on an energy level diagram?

Answer 15

The initial curve. The activation energy is the distance between the reactants and the turn in the curve.

Question 16

What is a catalyst?

Answer 16

A substance that can speed up a reaction without being changed or used up by lowering the activation energy.

Question 17

How does a catalyst work?

Answer 17

It provides a different pathway for the reaction which requires less energy overall.

Question 18

What is energy measured in?

Answer 18

Joules

Question 19

What is energy transfer measured in?

Answer 19

Kilojoules per gram (kj/g) or kilojoules per mile (kj/mol)

Question 20

How can you measure energy transfer in a reaction?

Answer 20

By taking a reading with a thermometer and then mixing everything together in a polystyrene cup and then taking another measurement.

Question 21

While measuring the rate of reaction, how can you prevent the amount of energy lost to the surroundings?

Answer 21

By surrounding the polystyrene cup with cotton wool in a beaker and putting a lid on the cup.

Question 22

What is calorimetry?

Answer 22

Measuring the amount of energy released when a fuel is burnt by using it to heat water.

Question 23

How does one carry out calorimetry?

Answer 23

1) Put 50g of water in a copper can and record its temperature
2) Weigh a spirit burner consigning methylated spirits with its lid on
3) Put the spirit burner underneath the can and light the wick. Heat the water until the temperature reaches 50 degrees.
4) Weigh the spirit burner and lid again.

Question 24

What is the formula for energy transfer?

Answer 24

Q = m x c x Δt

Q = Energy transferred (J)

m = Mass of water (g)

c = Specific Heat Capacity (4.2)

Δt = Change in temperature

Question 25

Is the reaction between hydrogen and oxygen exothermic or endothermic?

Answer 25

Exothermic

Question 26

What is an advantage and three disadvantages of using hydrogen combustion engines in cars?

Answer 26

+Very clean as only produces water

• Special engine required which is expensive
• Another energy source is required to get the hydrogen
• Hydrogen is hard to store

Question 27

What is a fuel cell?

Answer 27

An electrical cell that uses hydrogen and oxygen to generate electricity.