DF1- Getting Energy From Fuels

Question 1

Define thermochemistry

Answer 1

Study of energy and heat associated with chemical reactions

Question 2

Define enthalpy change

Answer 2

The energy transferred to and from the surroundings in a reaction

Question 3

Exothermic reactions…

Answer 3

• give out energy to surroundings

Question 4

For exothermic reactions, is delta H positive or negative?

Answer 4

Negative

Question 5

Give examples of exothermic reactions

Answer 5

• combustion

- oxidation

Question 6

Endothermic reactions…

Answer 6

• take in energy from surroundings

Question 7

For endothermic reactions, is delta H positive or negative?

Answer 7

Positive

Question 8

What are the standard conditions under enthalpy change (delta H) is measured?

Answer 8

• 100 atms
• 298 K
• solution at concentration of 1 moldm-3

Question 9

What is ‘standard enthalpy change of a reaction’?

Answer 9

Enthalpy change for a reaction when molar quantities of the reactants react under standard conditions, with all reactants in standard state

Question 10

What is ‘standard enthalpy change of combustion’?

Answer 10

Enthalpy change for the complete combustion of 1 mole of a substance under standard conditions

Question 11

What is ‘standard enthalpy change of formation’?

Answer 11

Enthalpy change for formation of 1 mole of a substance from it elements in their standard states under standard conditions

Question 12

What is ‘standard enthalpy change of neutralisation’?

Answer 12

Enthalpy change for formation of 1 mole of water from the neutralisation of an acid and a base under standard conditions

Question 13

Define activation energy

Answer 13

Minimum energy required to start a reaction by the breaking of bonds

Question 14

What is the equation for measuring enthalpy change?

Answer 14

Energy transferred, q (kJ) = mass, m (g) x specific heat capacity, c x change in temp, delta T (K)

Question 15

Describe process of measuring enthalpy change in combustion of fuel

Answer 15

1. Alcohol is burnt in spirit burner, produces heat
2. Heats mass of water in copper calorimeter
3. Temperature is measured before and after, burner is weighed before and after to determine mass burned

Question 16

What are the problems with measuring enthalpy change, when not using specialist equipment (bomb calorimeter)?

Answer 16

• heat is lost to atmosphere

- incomplete combustion