TOPIC 5 - Energy Changes✅

Question 1

Sometimes the products of a reaction store more energy than the reactants. What does this mean?

Answer 1

The products have taken an energy from the surroundings during the reaction.

Question 2

What is an exothermic reaction? How is it shown?

Answer 2

Reaction which gives out energy to the surroundings. This is shown by a rise in temperature of the surroundings.

Question 3

Give two examples of exothermic reactions:

Answer 3

1) Burning fuels - combustion.2) Neutralisation reactions (acid + alkali).

Question 4

Exothermic reaction to have lots of every day uses. Give an examples.

Answer 4

Self heating cans of hot chocolate and coffee also use exothermic reactions between chemicals in their bases.

Question 5

What is an endothermic reaction? How is it shown?

Answer 5

Reaction which takes in energy from the surroundings. This is shown by a fall in temperature of the surroundings.

Question 6

Give two examples of endothermic reactions:

Answer 6

1) The reaction between citric acid and sodium hydrogencarbonate.2) Thermal decomposition (when a substance breaks down when its heated)

Question 7

Endothermic reactions have everyday uses. Give an example.

Answer 7

Sports injury packs - the chemical reaction allows the pack to become instantly cooler without having to put it in the freezer.

Question 8

Give the 5 steps to measuring the energy change of a chemical reaction:

Answer 8

1) Take the temperature of the reactants and mix them in a polystyrene cup.2) if the temperature of the solution rises during the reaction, record the highest temperature that it reaches. If the temperature falls, record the lowest temperature that it reaches.3) to find the temperature change, take away this temperature from the temperature of the reactants.4) if the temperature goes up, the reaction is exothermic. If the temperature goes down, the reaction is endothermic.5) to reduce the amount of energy lost to the surroundings, put a lid on the polystyrene cup and put the cup into a beaker of cotton wool

Question 9

The temperature change of a reaction depends on…

Answer 9

Different variables.

Question 10

Give the 6 steps to testing the effect of acid concentration on the temperature change of a neutralisation reaction between hydrochloric acid and sodium hydroxide:

Answer 10

1) Put 25cm cubed each of 10 dm cubes hydrochloride acid and sodium hydroxide in separate beakers.2) Place the beakers in a water bath set at 25degrees until they are both at the same temperature.3) Add the HCL followed by the NaOH to a polystyrene cup with a lid.4) Take the temperature out of the mixture every 30 seconds and record the highest temperature.5) Use your results to work out the temperature change of the reaction.6) Repeat these steps using 20g and then 30g of hydrochloric acid then compare your results to see how acid concentration affects the temperature change of the reaction.

Question 11

What is activation energy?

Answer 11

The minimum amount of energy the reactants need to have to react when they collide with each other.

Question 12

The greater the activation energy, the more…

Answer 12

Energy needed to start the reaction.

Question 13

Activation energy is needed to…

Answer 13

Start a reaction.

Question 14

What are Reaction Profiles?

Answer 14

Diagrams that show the difference between the energies of the reactants and products in a reaction and how much the energy changes over the course of the reaction.

Question 15

Reaction profiles are sometimes called…

Answer 15

Energy level diagrams.

Question 16

How can you tell if it’s an exothermic reaction on a reaction profile? (3)

Answer 16

Because the products are at a lower energy than the reactants. The difference in height between the reactants and the products shows the overall energy change in the reaction (energy given out).The rise in energy at the start shows the energy needed to start the reaction.

Question 17

How can you tell if it’s an endothermic reaction on a reaction profile? (2)

Answer 17

The products are at a higher energy than the reactants.The difference in height shoes the overall energy change during the reaction ( energy taken in ).