Chapter 8 -- Chemical Energies

Question 1

Enthalpy change

Answer 1

Heat energy change measured at constant temp

Usually 298K and 100kPa

Question 2

Standard enthalpy change of combustion

Answer 2

Enthalpy change measures at 100 kPa and specified temp (usually 298K) when one mole of substance is completely burned in oxygen

Question 3

Enthalpy change of combustion equation

Answer 3

Q= mc🔼T

n=m/M

🔼H = - Q/n

Question 4

Standard enthalpy change of neutralisation

Answer 4

🔼neut H

Enthalpy change when one mole of water is produced by neutralisation of acid with an alkali

Question 5

Standard enthalpy change of neutralisation equation

Answer 5

Q= mc🔼T

amount of acid neutralised = amount of water formed

Question 6

Q

Answer 6

Heat energy

Question 7

Standard enthalpy change of formation

Answer 7

🔼f H

Enthalpy change when one mole of a substance is formed from its elements in their standard states

Question 8

Hess’s law

Answer 8

Enthalpy change of a reaction is independent of the path taken in converting reactants into products - provided the initial and final conditions are the same in each case

Question 9

Bond enthalpy

Answer 9

🔼B H

Enthalpy change when one mole of a bond in the gaseous state is broken

XY (g) —> X (g) + Y (g)

Question 10

Mean bond enthalpy

Answer 10

Enthalpy change when one mole of a bond averaged out over many different molecules is broken

Question 11

Enthalpy change of reaction using mean bond enthalpies

Answer 11

🔼r H

E(bonds broken) -E(bonds made)