C5 - Energy Changes

What is an exothermic reaction?

A reaction that transfers energy to the surroundings

What happens to the temperature of the surroundings in an exothermic reaction?

The temperature increases

What are some examples of exothermic reactions?

Combustion, neutralisation, and Oxidation reactions

What is an endothermic reaction?

A reaction that takes in energy from the surroundings

What happens to the temperature of the surroundings in an endothermic reaction?

It decreases

What are some examples of endothermic reactions?

Thermal decomposition, photosynthesis

What type of reaction happens in a self- heating can or hand warmer?

Exothermic reaction

What type of reaction happens in a sports injury cold pack?

Endothermic

Temperature Change Practical

1. Use a measuring cylinder to measure 30 cm³ of dilute hydrochloric acid
   

2. Pour the acid into the cup and stand the polystyrene cup into a beaker
   

3. Use a thermometer to measure the temperature of the acid and record it on a table
   

4. Use measuring cylinder to measure 5 cm³ of sodium hydroxide solution and pour into the cup
   

5. Place plastic lid on the cup, put thermometer through the hole in the lid, and gently stir the solution

Continuation of practical

6. When the reading stops changing, record the highest temperature reached
   

7. Rinse out and dry the polystyrene cup
   

8. Repeat the whole experiment using 10 cm³ of sodium hydroxide solution
   

9. Carry out the experiment several times, increasing the volume of sodium hydroxide solution by 5 cm³ until you reach 40 cm³.
   

10. Repeat the whole experiment to get two sets of results. Use these to calculate a mean value for the maximum temperature reached for each volume, and then plot a results graph

What does a reaction profile show?

The energy changes during a chemical reaction

What has more energy in an exothermic reaction profile?

Reactants have more energy than products

What has more energy in an endothermic reaction profile?

Products have more energy than reactants

What is the activation energy?

The minimum amount of energy the reactants need to collide with each other and react

Exothermic Reaction Energy Profile

Endothermic Reaction Energy Profile

What happens to bonds during chemical reactions?

Bonds in reactants are broken

New bonds are made in products

What happens to the energy when bonds are broken?

Energy is taken in (endothermic)

What happens to the energy when bonds are made?

Energy is released (exothermic)

What units are bond energies measured in?

kJ/mol

What formula can be used to estimate energy change?

Energy change = Energy in (bonds broken) - energy out (bonds made)