Enthalpy

Question 1

Enthalphy

Answer 1

A measure of heat energy in a chemical system
Sometimes thought of as the energy stored with bonds
Cannot be measured but its changes can

Question 2

Conservation of energy

Answer 2

States energy cannot be created or destroyed - only transferred

Question 3

Enthalpy change, ΔH

Answer 3

ΔH = Enthalpy (H) of products - Enthalpy (H) of reactants

Question 4

Exothermic enthalpy changes (-ΔH)

Answer 4

From system (loses) –> surroundings (gains)
Releases heat energy
… so tempurature increases

Question 5

Endothermic enthalpy change (+ΔH)

Answer 5

From surroundings (loses) –> system (gains)
Takes in heat energy
… so tempurature decreases

Question 6

Standard enthalpy changes

Answer 6

Measured in standard conditions

ΔH varies under diff. conditions –> standard offers comparision between diff. reactions

Question 7

Standard ΔH

Answer 7

The change that accompanies a reaction in molar quantities shown in a chemical equation under standard conditions

Question 8

Standard Enthalpy Change of Formation

Answer 8

ΔH f.

- Enthalpy change that occurs when 1 mole of a compound is formed from its element in standard conditions

Question 9

Standard Enthalpy Change of Combustion

Answer 9

Δ H C °

- Enthalpy change that occurs when 1 mole of a substance reacts completely w/ oxygen in standard conditons

Question 10

Standard Enthalpy Change of Neutralisation

Answer 10

ΔHn⊖

- Enthalpy change that occurs with the reaction of an acid + base to form 1 mole of h2o in standard conditions