Topic 8 Energetics

Question 1

What are the 4 types of enthalpy change in year 1 energetics

Answer 1

1. Enthalpy change of reaction
2. Formation
3. Combustion
4. Neutralisation

Question 2

Define enthalpy change of reaction

Answer 2

Enthalpy change of a reaction occurring under standard conditions (according to the mole ratios in the reaction equation)

Question 3

Define enthalpy change of formation

Answer 3

Enthalpy change when 1 mole of substance is formed from elements in their standard states under standard conditions

Question 4

Define enthalpy change of combustion

Answer 4

Enthalpy change when 1 mole of a substance is completely burned in oxygen to make CO2 and H2O under standard conditions

Question 5

Define enthalpy change of neutralisation

Answer 5

Enthalpy change when an acid and alkali react to form one mole of water under standard conditions

Question 6

Is bond breaking exo or endo

Answer 6

Endothermic

Question 7

Why are calculations with mean bond enthalpy inaccurate in comparison to theoretical values

Answer 7

Theoretical values take into account specific location in a molecule and how bond enthalpy changes when bonds around it have already been broken.

Question 8

What do you use to work out enthalpy change of combustion

Answer 8

Calorimeter - fuel is weighed before and after and temperature change is measured - plug into q=mcdetlaT

Question 9

How to improve calorimeter accuracy

Answer 9

Lid, insulating materials, bomb calorimeter

Question 10

Energy change formula and units

Answer 10

q=mc deltaT
q = J
m = g ( of water )!!!!
c = 4.18
T = K

Question 11

How to get enthalpy change from q

Answer 11

-q/(1000 x n)

Question 12

What is Hess’ law

Answer 12

Enthalpy change in a reaction is independent of the route taken