enthalpy changes

Question 1

exothermic reaction

Answer 1

heat energy is released to the surroundings (ΔH is negative)

Question 2

endothermic reaction

Answer 2

heat energy is absorbed from the surroundings (ΔH is positive)

Question 3

average bond enthalpy

Answer 3

average enthalpy change for the breaking of one mole of bonds in gaseous molecules

Question 4

standard conditions

Answer 4

298K
101kPa
1.0moldm-3

Question 5

enthalpy change of neutralisation

Answer 5

enthalpy change when one mole of water is formed by neutralisation

Question 6

enthalpy change of formation

Answer 6

enthalpy change when one mole of a compound is formed from its elements

Question 7

enthalpy change of combustion

Answer 7

enthalpy change when one mole of a compound undergoes complete combustion

Question 8

hess’ law

Answer 8

the enthalpy change of a reaction depends only on the initial and final states and is independent of the route taken

Question 9

homolytic fission

Answer 9

bond breaks evenly to form two radicals

Question 10

heterolytic fission

Answer 10

bond breaks unevenly to form two ions

Question 11

enthalpy change of reaction

Answer 11

ΔrH = ΔH(breaking bonds) - ΔH(forming bonds)

Question 12

enthalpy changes when making/breaking bonds

Answer 12

mexo bendo
making bonds is exothermic
breaking bonds is endothermic

Question 13

using ΔfH data

Answer 13

use fliPpeR
arrows upwards
products - reactants

Question 14

using ΔcH data

Answer 14

use cRaP
arrows downwards
reactants - products

Question 15

calculating enthalpy change of reaction from experimental data

Answer 15

q = mcΔt
ΔH = q / n