5 Energetics

Question 1

Specific heat capacity (of solutions unless stated otherwise)

Answer 1

4.18 Jg^-1K^-1

Question 2

Calc for enthalpy change using heat of reaction.

Answer 2

Enthalpy change = ( mass(g) x C(4.18) x change in temp ) / 1000 x moles of whatever’s produced/burnt

Question 3

standard enthalpy change of reaction formula

Answer 3

= standard enthalpy change of formation of PRODUCTS - REACTANTS

Question 4

Limitations of using temp to calc enthalpy change

Answer 4

Significant heat lost to surroundings

Question 5

Limitations of bond enthalpy method

Answer 5

Bond enthalpy values are calculated based on gaseous covalent bonds — if molc in other state, bond enthalpy value will be inaccurate

Question 6

definition of standard enthalpy change of Formation triangle H ^0 f

Answer 6

enthalpy change when ONE MOLE of a compound is FORMED from its elements
in their standard states under standard conditions of 298K and 100 pKa

Question 7

definition of standard enthalpy change of combustion

Answer 7

enthalpy change when ONE MOLE of a substance in its standard state is COMPLETELY BURNED in EXCESS OXYGEN under standard conditions

Question 8

definition of standard enthalpy change of neutralisation

Answer 8

enthalpy change when ONE MOLE of water is FORMED between the neutralisation of an acid and base under standard conditions

Question 9

heat change formula

Answer 9

Q = m c (Triangle)T
mass x heat capacity x change in temperature

Question 10

enthalpy change formula

Answer 10

-/+ heat change / moles of limiting reagent

Question 11

formula of ethanol

Answer 11

C2H6O

Question 12

formula of ethanoic acid

Answer 12

CH3COOH

Question 13

hess’ law is based on

Answer 13

law of conservation of energy – the enthalpy change of a chemical reaction is the same whether the change is brought about thru 1 or many stages

Question 14

bond enthalpy definition

Answer 14

energy needed to BREAK ONE MOL of BONDS in the gaseous molecules, under standard conditions

Question 15

enthalpy change of reactants using BOND ENERGIES (only for GAS)

Answer 15

= bonds broken in REACTANTS - formed in PRODUCTS

Question 16

lattice energy definition

Answer 16

the standard enthalpy change when ONE MOLE of a SOLID IONIC compound is seperated into GASEOUS ions under standard conditions

Question 17

lattice energy process is (endo/exo)

Answer 17

endothermic
greater lattice energy, stronger the ionic bond

Question 18

what does magnitude of lattice energy depend on

Answer 18

• charge of ions
• size of ions
• arrangement of ions in solid

Question 19

definition standard enthalpy change of atomisation

Answer 19

the standard enthalpy change when ONE MOLE of GASEOUS atoms is formed from the element in its natural states

Question 20

definition standard enthalpy change of hydration

Answer 20

the standard enthalpy change when ONE MOLE of gaseous ions forms ONE MOLE of HYDRATED ions in water under standard conditions

Question 21

factors affecting standard enthalpy change of hydration 2

Answer 21

size and charge of ions

Question 22

definition standard enthalpy change of solution

Answer 22

standard enthalpy change when ONE MOLE of a SOLUTE is DISSOLVED in a SOLVENT to INFINTE DILUTION under standard conditions

Question 23

calculation of 7H of solution

Answer 23

= 7H lattice + 7H hydration

Question 24

gibbs free energy calc

Answer 24

7G = 7H - Tx7S

standard enthalpy change - temp in K x standard entropy change (+ or -)

Question 25

gibbs calc using products and reactants

Answer 25

= G prodcuts - G formation

Question 26

when G is neg, forward reaction is

Answer 26

spontaneous

Question 27

when G is pos, forward reaction is

Answer 27

not spon BUT backward reaction is

Question 28

G is affected by

Answer 28

temperature
H and S of reaction cannot change

Question 29

when reaction is equilibirum, entropy and G are

Answer 29

• maximum
• zero – both reactions are spontaneous