Energy Changes

Question 1

What is the conservation of energy?

Answer 1

• amount of energy at the end of reaction = amount of energy after reaction
• reaction transfers energy to surroundings = product has less energy than reactants

Question 2

What is activation energy?

Answer 2

• minimum amount of energy that particles must have to react

Question 3

What is an exothermic reaction?

examples and uses

Answer 3

• reaction that transfers energy to surroundings
• temperature of surroundings increase
• eg combustion, oxidation, neutralisation
• self-heating cans, hand warmers

Question 4

What is an endothermic reaction?

examples and use

Answer 4

• reaction that takes in energy from surroundings
• temperature of surroundings decrease
• eg thermal decomposition

used in sports injury packs

Question 5

How do you measure energy change?

Answer 5

1) put polystyrene cup into beaker for stability
2) use measuring cylinder to measure 25cm^3 of hydrochloric acid into cup
3) insert thermometer bulb into solution and clamp thermometer
4) put lid on cup (keep heat in)
5) record initial temp of solution
6) add in 5 cm^3 of sodium hydroxide
7) stir solution, measure temp
8) repeat 6 and 7 until all NaOH added

Question 6

How do you prevent heat loss to the surroundings?

Answer 6

• insulate vessel
• lid

Question 7

How do you record an accurate temperature?

Answer 7

• stir mixture
• immerse bulb of thermometer

Question 8

How do you measure accurate volumes

Answer 8

• use measuring cyclinder

Question 9

What should the results be like for the energy change in neutralisation?

Answer 9

• temperature rises with each addition
• until all acid has reacted
• further additons cool solution down

Question 10

How do chemical reactions occur?

Answer 10

• when reacting particles collide with each other and with sufficient energy

Question 11

Draw the reaction profile of an exothermic reaction

Question 12

Draw the reaciton profile of an endothermic reaction