Topic 5 Energy Changes

Question 1

What is an exothermic reaction?

Answer 1

1. In an exothermic reaction, heat is given out.
2. It transfers energy to the surroundings, usually by heating. This is shown by a rise in temperature.

Question 2

Examples of exothermic reactions?

Answer 2

1. Burning fuels - combustion.
2. Neutralisation reactions.
3. Many oxidation reactions.

Question 3

Every-day uses of exothermic reactions?

Answer 3

1. Some hand warmers use exothermic reactions of iron in air.
2. Self heating cans also rely on exothermic reactions.

Question 4

What is an endothermic reaction?

Answer 4

1. In an endothermic reaction, heat is taken in.
2. It takes in energy from the surroundings. This is shown by a fall in temperature.

Question 5

Which reaction is more common?

Answer 5

1. Exothermic reactions are much more common than endothermic reactions.

Question 6

Examples of endothermic reactions?

Answer 6

1. The reaction between citric acid and sodium hydrogencarbonate.
2. Thermal decomposition. E.g. heating calcium carbonate causes it to decompose into calcium oxide (quicklime) and carbon dioxide.

Question 7

Every-day uses of endothermic reactions?

Answer 7

1. Sports injury packs

Question 8

Method to measure energy transfer based on acid concentration?

Answer 8

1. Put 25cm of 0.25mol/dm of HCL and sodium hydroxide in separate beakers.
2. Place the beakers in a water bath set to 25 degrees celcius until they are both the same temperature.
3. Add the HCL followed by the NaOH to a polystyrene with a lid.
4. Take the temperature of the mixture every 30 seconds, and record the highest temperature.
5. Repeat steps 1-4 using 0.5 mol/dm and then 1 mol/dm of HCL.

Question 9

How would you improve the energy transfer method?

Answer 9

1. Reduce energy lost to surroundings by putting the polystyrene cup into a beaker of cotton wool to give more insulation.
2. Place a lid on top to reduce energy lost by evaporation.