8 - energetics

Question 1

exothermic

Answer 1

heat energy is transferred from the system to the surroundings

Question 2

endothermic

Answer 2

heat energy is transferred from the surroundings to the system

Question 3

standard enthalpy change of reaction

Answer 3

is the enthalpy change when substances react under standard conditions (usually 100kPa and 298K) in quantities(moles) given by the equation

Question 4

standard enthalpy change of combustion

Answer 4

is the enthalpy change measured in standard conditions when one mole of a fuel is completely burned in oxygen

Question 5

standard enthalpy change of neutralisation

Answer 5

is the enthalpy change in standard conditions when one mole of water is produced through the neutralisation of an acid and an alkali

Question 6

standard enthalpy change of formation

Answer 6

is the enthalpy change in standard conditions when one mole of a substance/compound is formed from its elements in their standard states

Question 7

Hess’s Law

Answer 7

states that the 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 8

bond enthalpy

Answer 8

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

Question 9

mean bond enthalpy

Answer 9

is the enthalpy change when one mole of a bond, averaged out over many different molecules is broken

Question 10

energy equation and units

Answer 10

Q = mc Δt
energy (J) = mass (g) x specific heat capacity x change in temp

Question 11

ΔH equation

Answer 11

ΔH = Q/1000 / mol
units - kJ/mol

ΔH = Ein - Eout

Question 12

enthalpy change

Answer 12

the amount of heat energy taken in or given out during any change in a system providing the pressure is constant.