5.1 Measuring energy changes

Question 1

Enthalpy

Answer 1

Amount of energy content of a substance stored in chemical bonds

Includes kinetic and potential energy
Measured indirectly through changes

Question 2

Standard enthalpy change of reaction

Answer 2

Difference between the enthalpy of the reactants and products at 298K and 1 * 10⁸ pa

Question 3

Specific heat capacity of a substance

Answer 3

Amount of energy needed to raise the temperature of 1Kg of substance by 1 Kelvin

Question 4

Bond enthalpy

Answer 4

Amount of energy required to break one mole of bonds in the gaseous state averaged across a range of compounds containing that bond.

Question 5

Energy change when breaking bonds

Answer 5

Endothermic

Question 6

Energy change when making bonds

Answer 6

Exothermic

Question 7

Stability and bond enthalpy of exothermic reaction

Answer 7

Exothermic reaction=energy lost by bonds=bonds more stable=higher bond enthalpies

Question 8

Stability and bond enthalpy of endothermic reaction

Answer 8

Endothermic=bonds gained energy=bonds less stable=lower bond enthalpies

Question 9

Hess’s law

Answer 9

In a chemical reaction total enthalpy change must be equal to energy lost or gained by the reaction system

Enthalpy change for a reaction is always the same, no matter the route taken from reactants to products.

Question 10

Standard enthalpy of formation

Answer 10

Enthalpy change when one mole of compound is formed from its elements at 298K and 1.0 * 10⁸ Pa

All reactants and products in standard state

Question 11

Standard enthalpy of combustion

Answer 11

Enthalpy resulting when 1 mole of compound reacts with oxygen at 298K and 1.0 * 10⁸ Pa

All reactants and products in their standard state