C9 - Thermodynamics

Question 1

What are the three methods for calculating enthalpy changes

Answer 1

Average bond enthalpies
Q=mc delta t
Hess cycles

Question 2

What is the equation linking mass and temperature change to enthalpy and what are its units

Answer 2

Q=mc delta t
Q= J
M= kg
T= K but doesn’t matter

Question 3

Define enthalpy change of formation

Answer 3

Enthalpy change when one mole of a substance is formed from its constituent elements with all reactants and products in standard states under standard conditions

Question 4

Define enthalpy change of combustion

Answer 4

Enthalpy change when one mole of a substance is completely burned in oxygen with reactants and products in the standard states under standard conditions

Question 5

Define enthalpy change of neutralisation

Answer 5

Enthalpy change when one mole of water is formed in a reaction between an acid and an alkali under standard conditions

Question 6

Define average bond enthalpy

Answer 6

Energy required to break one mole of bonds