Topic 13: Energetics II (i need to add entropy as we do it)

Question 1

What is the formula for q? (calorimetry)

Answer 1

q=mcΔT

Question 2

What does each of the variables represent and its units in q=mcΔT

Answer 2

q = heat transferred (J)
m = mass [of water!!] (g)
c = specific heat capacity [of water] J/(K g)
ΔT = change in temp (C or K is fine)

Question 3

Enthalpy change of solution

Answer 3

Enthalpy change when one mole of a solute is dissolved in enough solvent such that no further ΔH when diluted further.

Question 4

Enthalpy change of hydration

Answer 4

Enthalpy change when one mole of gaseous ions form one mole of aqueous ions

Question 5

What are the effects of ionic charge and radius on ΔHhyd

Answer 5

The higher the charge density the higher the ΔHhyd as the ions attract water molecules more strongly.

Question 6

Is ΔHhyd exothermic or endothermic and why?

Answer 6

ΔHhyd is exothermic as energy is released when water molecules interact with ions.

Question 7

What is the implication of a positive ΔHsol

Answer 7

The ions form stronger interactions with each other than with water.

Question 8

What does lattice enthalpy tell us?

Answer 8

The strength of the ionic bonds.

Question 9

What is the formula for ΔS(tot)

Answer 9

ΔS(tot) = ΔS(sys) + ΔS(surr)

Question 10

What is the formula for ΔS(surr)

Answer 10

-ΔH/T

Question 11

What is the formula for Gibbs free energy

Answer 11

ΔG = ΔH - TΔS

Question 12

What is the difference between feasibility and spontaneity

Answer 12

feasability: a reaction can happen,
spontaneity: a reaction happens on its own

Question 13

What is the difference between kinetic and thermodynamic stabilityy

Answer 13

Kinetically stable : high activation energy
Thermodynamically stable : reactants are lower energy than the products

Question 14

What are the units for entropy

Answer 14

JK-1mol-1

Question 15

What are the units for ΔH

Answer 15

kJmol-1

Question 16

What is the relationship between the equilibrium constant, K, and ΔS_tot

Answer 16

ΔS_tot = R * ln(K)

Question 17

What is the relationship between ΔG and the equilibrium constant, K

Answer 17

ΔG = - R T ln(K)

Question 18

What is the relationship between E_cell, ΔS, and ln K

Answer 18

E_cell ∝ ΔS ∝ lnK