Topic 8 - energetics

Question 1

Define enthalpy change

Answer 1

The heat change measured under conditions of constant pressure

Question 2

What are standard conditions?

Answer 2

100 kPa
Stated temp which is usually 298K

Question 3

Define standard enthalpy of combustion

Answer 3

The enthalpy change where one mole of a substance is burned completely in oxygen under standard conditions, with all reactants and products in their standard states.

Question 4

Define standard enthalpy of formation

Answer 4

The enthalpy change where one mole of a substance is formed from its elements under standard conditions, with all reactants and products being in their standard states.

Question 5

Define Hess’ law

Answer 5

The enthalpy change of a reactions depends only on the initial and final states of the reaction and is independent of the route by which the reaction occurs.

Question 6

Define mean bond enthalpy

Answer 6

The enthalpy change when one mole of a covalent bond is broken, with all species in the gaseous state, averaged over a range of different compounds.

Question 7

Breaking bonds is?

Answer 7

Endothermic

Energy is required
Enthalpy change is positive

Question 8

Making bonds is?

Answer 8

Exothermic

Energy is released
Enthalpy change is negative