5..., 15..

Question 1

Heat

Answer 1

q
is form of energy that flows down the temperature gradient from an object of higher temperature to an object of lower temperature

Question 2

Calorimeter

Answer 2

• an apparatus used to measure the amount of heat being exchanged with surroundings

Question 3

specific heat capacity

Answer 3

amount of heat required to raise the temperature of one gram of a substance by one degree Celsius

Question 4

Temperature

Answer 4

is a measure of the average kinetic energy of particles
absolute temperature (in kelvin) = temp (Celsius) + 273

Question 5

Bond breaking

Answer 5

requires energy
endothermic
heat is absorbed

Question 6

bond making

Answer 6

releases energy
exothermic
Heat is released

Question 7

Systems

Answer 7

Open system – matter and energy can be transferred between the system and surroundings.
Closed system – energy can be transferred between the system and surroundings but matter cannot.
Isolated system – neither matter nor energy can be transferred between the system and surroundings.

Question 8

exothermic reactions

Answer 8

• – ∆H
• ## heat is transferred from the system to the surroundings

Question 9

Endothermic

Answer 9

• ∆H
• heat is absorbed from the surroundings

Question 10

Enthalpy change of combustion

Answer 10

(ΔHѳc) is the enthalpy change upon complete combustion of 1 mol of a substance.
always negative as heat is released during combustion
reactants - products

Question 11

enthalpy change of formation

Answer 11

is the enthalpy change upon formation of 1 mol of a substance from its elements
products - reactants

Question 12

Limitations of Calculating enthalpy changes

Answer 12

• Heat loss to surroundings
• Incomplete combustion
• Assumptions made about specific heat capacity and density of aqueous solution

Question 13

Hess’ Law

Answer 13

the total enthalpy change in a chemical reaction is independent of the route by which the chemical reaction takes place, as long as the initial and final conditions are the same.
The enthalpy change for a reaction that is carried out in a series of steps is equal to the sum of the enthalpy changes for the individual steps.

Question 14

Average bond enthalpy

Answer 14

enthalpy change when one mole of bonds are broken in
the gaseous state, averaged for the same bond in similar compounds
reactants - products

Question 15

Limitations of average bond enthalpy calculations

Answer 15

Enthalpy changes calculated from average bond enthalpies may be different than enthalpy changes calculated from actual values due to the averaging.
Calculations involving bond enthalpies may be inaccurate because they do not take into account intermolecular forces.

Question 16

Ozone layer

Answer 16

• The ozone layer in Earth’s atmosphere absorbs harmful UV radiation from the sun. The ozone is in dynamic equilibrium with oxygen and is continually being formed and destroyed.
• The covalent bond in oxygen (O2) is broken by UV radiation. A free radical is a highly reactive species due to the presence of an unpaired electron ().
  O2 (g) → O (g) + O* (g)
• The highly reactive free radical oxygen atoms react with oxygen (O2) to form ozone (O3).
  O2 (g) + O* (g) → O3 (g)
• Ozone decomposes to form oxygen (O2) and an oxygen free radical. The bonds in the ozone (O3) molecules are weaker than the double bonds in oxygen (O2), so they can be broken by lower energy UV radiation.
  O3 (g) → O2 (g) + O* (g)

Question 17

Lattice Enthalpy

Answer 17

The standard enthalpy change that occurs on the formation of 1 mol of gaseous ions from the solid lattice. The symbol is ΔHѳlat
- endothermic
- + value

NaCl (s) → Na+ (g) + Cl- (g) ΔHlatꝋ = +790 kJ mol -1

Question 18

Ionisation energy

Answer 18

standard enthalpy change that occurs on the removal of 1 mole of electrons from 1 mole of gaseous atoms or positively charged ions
- endothermic
- + value

ΔHIE1ꝋAl (g) → Al+ (g) + e– ΔHIE1ꝋ = +577 kJ mol-1

Question 19

Enthalpy atomisation

Answer 19

standard enthalpy change that occurs on the formation of 1 mole of separate gaseous atoms an element in its standard state
- endothermic
- + value

Na (s) → Na (g) ΔHatꝋ = +108 kJ mol -1
½Cl2 (g) → Cl (g) ΔHatꝋ = +122 kJ mol -1

Question 20

Electron Affinity

Answer 20

energy change when 1 mole of electrons is gained by 1 mole of gaseous atoms of an element to form 1 mole of gaseous ions under standard conditions
- first: exothermic

Cl (g)+ e– → Cl– (g) ΔHEAꝋ = -364 kJ mol-1

• second: endothermic

O– (g) + e– → O2- (g) ΔHEAꝋ = +844 kJ mol-1

Question 21

Enthalpy of solution

Answer 21

enthalpy change when 1 mole of an ionic substance dissolves in sufficient water to form an infinitely dilute solution
- can be exothermic or endothermic

LiBr (s) → LiBr (aq) ΔHsolꝋ = -48.8 kJ mol -1

KCl (s) → KCI (aq) ΔHsolꝋ = +17.2 kJ mol -1

Question 22

Enthaloy of Hydration

Answer 22

nthalpy change when 1 mole of a specified gaseous ion dissolves in sufficient water to form an infinitely dilute solution
Mg2+ (g) → Mg2+ (aq) ΔHhydꝋ = -1963 kJ mol -1

Br- (g) → Br- (aq) ΔHhydꝋ = -328 kJ mol -1

• exothermic

Question 23

Born-Haber cycles

Answer 23

a specific application of Hess’s Law for ionic compounds and enables us to calculate lattice enthalpy, which cannot be found by experiment
The basic principle of drawing the cycle is to construct a diagram in which energy increases going up the diagram

Question 24

Born-Haber cycle calculations

Answer 24

ΔHfꝋ = ΔHatꝋ + ΔHatꝋ + IE + EA - ΔHlattꝋ

or

ΔHfꝋ = ΔH1ꝋ - ΔHlattꝋ
where ΔH1ꝋ is the sum of all of the various enthalpy changes necessary to convert the elements in their standard states to gaseous ions

Question 25

Entropy

Answer 25

A measure of the distribution of available energy among the particles. The more ways energy can be distributed, the higher the entropy.

gases have more entropy than solids

Question 26

Spontaneous changes regards to entropy

Answer 26

entropy increases as state changes from solid to liquid to gas

Question 27

Gibbs free energy and spontaneouse reactions

Answer 27

An equation to combine enthalpy, entropy, and temperature of a system
ΔGѳ = ΔHѳ – TΔS
For reaction to be spontaneous, Gibbs Free energy must have negative value

Question 28

Gibbs free energy

Answer 28

Represents the free energy change when 1 mol of a compound is formed from its elements under standard conditions
If the Gibbs free energies of formation are not known, use enthalpy and entropy data.
ΔGѳ = ΔHѳ – TΔS

Question 29

Spontaneity (ΔGѳ = ΔHѳ – TΔS)

Answer 29

Question 30

Spontaneity (ΔGѳ = ΔHѳ – TΔS)

Answer 30

Question 31

energy transferred

Answer 31

Q is in joules