DF 1 - Developing fuels

Question 1

What is thermochemistry?

Answer 1

The study of energy and heat associated with chemical reactions. (Different fuels give out different amounts of energy when one mole is burnt.)

Question 2

Are fuels energy sources?

Answer 2

They can be thought of as energy sources but they can’t release energy until they have combined with oxygen - so fuel-oxygen systems should be thought of as the energy sources

Question 3

What is an exothermic reaction?

Answer 3

A reaction that gives out energy and heats its surroundings (increases in temp.)

Question 4

What is an endothermic reaction?

Answer 4

A reaction that takes in energy and cools surroundings (decreases in temp.)

Question 5

Draw an enthalpy level diagram for an exothermic reaction

Answer 5

x-axis: progress of reaction
y-axis: enthalpy
Reactants have more energy than the products
The energy is given out to surroundings so the enthalpy change is negative

Question 6

Draw an enthalpy level diagram for an endothermic reaction

Answer 6

x-axis: progress of reaction
y-axis: enthalpy
Reactants have less energy than the products
Energy is taken in from the surroundings so the enthalpy change is negative

Question 7

What 3 things need to be regulated in standard conditions?

Answer 7

Temperature, pressure and concentration

Question 8

What is 0 degrees in kelvin?

Answer 8

273 K

Question 9

What are the conditions for standard enthalpy change for a reaction?

Answer 9

Pressure: 100 kPa
Temperature: 298 K (25 degrees)
All substances in their standard states
Concentration: 1 mol/dm^3

Question 10

What is the equation for enthalpy change?

Answer 10

Enthalpy change = mass x specific heat capacity x change in temp.

Question 11

What is the specific heat capacity of water?

Answer 11

4.18 J per g per K

Question 12

What is the units for enthalpy change?

Answer 12

kJ per mol

Question 13

Why is enthalpy change of combustion (at standard conditions) less exothermic?

Answer 13

• Incomplete combustion
• Loss of energy to surroundings (biggest factor)
• Experiment not done at standard conditions

Question 14

How do improve the accuracy of the reaction?

Answer 14

• Add a wind shield
• Lid
• Insulation (e.g wool around beaker)

Question 15

What does a bomb calorimeter do?

Answer 15

It burns fuel electrically with oxygen in a pressurised vessel so that complete combustion can happen. Energy is transferred to the surrounding water where temperature rise is measured.

Question 16

What does a bomb calorimeter do?

Answer 16

It burns fuel with oxygen so that complete combustion can happen

Question 17

What does a bomb calorimeter do?

Answer 17

It burns fuel with oxygen so that complete combustion can happen

Question 18

What is it made up of?

Answer 18

It is made up of:

• bomb
• platinum resistance thermometer
• thermostat (to control heat)
• stirrers
• thermostatted outer tank of water
• calorimeter full of water

Question 19

What is the standard enthalpy change of combustion?

Answer 19

It is the enthalpy change that occurs when one mole of a substance is burnt completely in oxygen under standard conditions in standard states

Question 20

What is standard enthalpy change of formation?

Answer 20

It is the enthalpy change when one mole of a compound is formed from its elements under standard conditions in standard states

Question 21

Is the enthalpy change of combustion positive or negative?

Answer 21

Negative - it is an exothermic reaction so it loses energy to the surroundings

Question 22

What is the standard enthalpy change of neutralisation?

Answer 22

It is the enthalpy change when one mole of H+ ions react with one mole of OH- ions to form one mole of water under standard conditions and in solutions containing 1 mol/dm^3

Question 23

Is a neutralisation reaction endothermic or exothermic?

Answer 23

Exothermic - energy is given out