Energetica I

Question 1

Enthalpy definition

Answer 1

Enthalpy is heat energy change measured at constant pressure. The symbol for enthalpy is H.

Question 2

Endothermic definition

Answer 2

Endothermic changes are those that take in energy from their surroundings.

Question 3

Exothermic definition

Answer 3

Exothermic changes are those that give out energy to their surroundings.

Question 4

ΔH definition

Answer 4

ΔH (“delta H”) means ‘enthalpy change’.

Question 5

Standard conditions (ɵ) definition

Answer 5

Standard conditions (ɵ) are the ‘standard’ at which enthalpy changes are measured and are: 100kPa, 298K. ΔHɵ means ‘standard enthalpy change’.

Question 6

Callrimetry definition

Answer 6

Calorimetry is an experimental method to find the enthalpy change in a chemical reaction.

Question 7

Standard enthalpy of combustion definition

Answer 7

Standard enthalpy of combustion is the enthalpy change when one mole of a substance burns completely in oxygen under standard conditions (298K, 100kPa), with all reactants and products in their standard states

Question 8

Standard enthalpy of formation definition

Answer 8

Standard enthalpy of formation is the enthalpy change when one mole of a substance forms from its constituent elements under standard conditions (298K, 100kPa), with all reactants and products in their standard states

Question 9

Standard enthalpy of neutralisation

Answer 9

Standard enthalpy of neutralisation is the enthalpy change when one mole of water is produced in a neutralisation reaction between an acid and an alkali under standard conditions (298K, 100kPa). [note: not standard states because will be aqueous]

Question 10

Standard enthalpy of reaction definition

Answer 10

Standard enthalpy of reaction is the enthalpy change when the number of moles of substances shown by an equation as written react under standard conditions (298K, 100kPa), with all reactants and products in the states given.

Question 11

Hess’s law definition

Answer 11

Hess’s Law states that the enthalpy change for a given reaction is the same, independent of the route by which this is achieved (provided the temperatures, pressures, and physical states of products and reactants are the same).

Question 12

Bond enthalpy definition

Answer 12

Bond enthalpy is the energy required to break one mole of bonds, in the gaseous state.

Question 13

Mean bond enthalpy definition

Answer 13

Mean bond enthalpy is the energy required to break one mole of bonds, in the gaseous state, averaged across a range of compounds.