Chemistry (Thermodynamics)

Question 1

Heat and temperature

Answer 1

Heat: Total energy applied.
Temperature: Average kinetic energy

Temperature ∝ Kinetic ∝ Velocity
Heat in joules and temp in Kelvins.

Liquid to gas
q= m (ΔH vaporation)

Solid to liquid
q= m(Δ fusion)

Question 2

Heat capacity

Answer 2

calculating (q) of gas, solid, liquid heating up

Phase change: Q = m•ΔH(vap/fus)
Temp. Based: Q= m•C (specific heat)•ΔT

Question 3

Calorimetry

Answer 3

Calorimeter measures heat exchange

1) heat lost is heat gained by another
a. -q lost = q gain
2) Adiabatic: no heat gained or lost.
3) Coffee cup calorimeter: constant pressure (gas can escape).
4) Calorie: amount of energy needed to increase 1g of water by 1°C
5) bomb calorimeter: constant volume

Q rxn= Q water (reaction will produce heat and be absorbed by water)

How to measure heat of water
Q rxn = m•Cp•ΔT water

Question 4

STP and Standard conditions

Answer 4

STP: 0°C, 1atm. Used for ideal gas law

Standard Conditions: 25°C, 1atm. Used for G °, S °, H °, and E °

Question 5

Enthalpy

Answer 5

Change in energy in a system

• Reactant molecules: bonds broken (energy in (+))
• Product molecules: bonds formed (energy out (-))
• equation: ΔH= Σin - Σout/ Σbonds broken - Σbonds formed.

Question 6

Calculating ΔH: Bond Dissociation

Answer 6

Ereactants - Eproducts

2H2 + O2 —> 2H2O    
						H-H: 435 KJ/mol
						O-H: 460 KJ/mol
						O-O: 500 KJ/mol
2(435) + (500) - 4(460)

Question 7

Calculating ΔH: Heat of formation

Answer 7

ΔH= ΣHf products- ΣHf reactants

• zero for elements in standard state.
• Hf must be given
• fractions can be used.

Question 8

Hess’ Law

Answer 8

Combine couple of reactions to form something new and individual enthalpies will add up.

Question 9

Entropy

Answer 9

Number of things and space they occupy

Entropy: S= K (Boltzmann’s constant)•ln Ω

Loss of gas’s impacts entropy

Question 10

Changes in entropy

Answer 10

ΔS= Σproducts - Σ reactants.

ΔS= ΔQ/T

Question 11

Laws of thermodynamics

Answer 11

0th: ΔT means energy will flow
1st: energy always conserved (E= Q +W)
2nd: Entropy always increasing
3rd: Entropy of a solid at 0 Kelvins is zero!

Question 12

Gibbs Free Energy

Answer 12

ΔG rxn= Gprod - G react

Gibbs free energy used to determine reaction spontaneity.
- ΔG>0 non spontaneous (+), ΔG<0 spontaneous (-), ΔG=0 equilibrium

Question 13

Equilibrium using G

Answer 13

ΔG = ΔG° + RT ln Q
@equilibrium ΔG= 0 and Q= keq
∴ ΔG° = -RT ln (Keq)