energy transfer

Question 1

What is an exothermic reaction?

Answer 1

One which gives out heat energy (rise in temperature)

Question 2

What is an endothermic reaction?

Answer 2

One which takes in heat energy (fall in temperature)

Question 3

What is enthalpy change?

Answer 3

Overall change in energy of a reaction. Symbol is /\ H
Exothermic reactions –> negative value
Endothermic reactions –> positive value

Question 4

Does breaking bonds give out energy or take it in?

Answer 4

Takes in energy (B-end = breaking is endothermic)

Question 5

Does making new bonds give out or take in energy?

Answer 5

Gives out energy (M-ex = making is exothermic)

Question 6

What is the activation energy for a reaction?

Answer 6

Minimum energy needed by particles for reaction to occur (shown as initial rise on energy level diagram)

Question 7

If products have lower energy level than reactants, what sort of reaction is it?

Answer 7

Exothermic (negative enthalpy change)

Question 8

If products have higher energy level than reactants, what sort of reaction is it?

Answer 8

Endothermic (positive enthalpy change)

Question 9

What is the effect of a catalyst on energy level diagram?

Answer 9

Makes reaction happen faster by providing alternative reaction pathway with lower activation energy. But OVERALL ENERGY CHANGE REMAINS THE SAME

Question 10

How can you measure enthalpy change using calorimetry? (Dissolving, displacement & neutralisation)

Answer 10

1. Take temperature of reactants in polystyrene cup
2. Mix reactants together
3. Take temperature of solution after reaction
4. Minimise heat loss by using lid and insulation

Question 11

How can you measure amount of energy produced when fuel is burned?

Answer 11

1. Put 50g of water in copper can and take temperature
2. Weigh spirit burner and lid
3. Heat water with spirit burner till it gets to c 50 degrees
4. Measure final temperature of water
5. Weigh spirit burner and lid again
6. Use measurements to calculate enthalpy change

Question 12

How do you calculate heat energy transferred?

Answer 12

4.2 x 50 (if using 50g of water) x rise in temperature

Then divide by number of grams of fuel burned

Question 13

What is a reversible reaction?

Answer 13

One where products of reaction can themselves react to produce original reactants

Question 14

Explain why thermal decomposition of ammonium chloride is a reversible reaction

Answer 14

1. White solid breaks down into gases ammonia and hydrogen chloride.
2. When gases cool they react to reform the white solid

Question 15

What is dynamic equilibrium?

Answer 15

Reactions are still taking place in both directions but forward and reverse reactions cancel each other out. Reactions are taking place at exactly the same rate.

Question 16

What happens if you increase temperature in reversible reaction?

Answer 16

Changing temperature will move position of equilibrium. 1. Raising temperature will increase endothermic reaction
2. Reducing temperature will increase exothermic reaction

Question 17

What happens if you increase pressure in reversible reaction?

Answer 17

1. Raising pressure will increase reaction which produces less volume
2. Reducing pressure will increase reaction which produces more volume