Chem 202 Test 2

1st thermo law

ΔE_universe = ΔE_system + ΔE_surroundings = 0

ΔE_system = q + w

q < 0

q > 0

w > 0

w < 0

q < 0 : heat is released by the system (exothermic)

q > 0 : heat is absorbed by the system (endothermic)

w > 0 : work is done on the system

w < 0 : work is done by the system

What is work measured in?

joules

in a work problem, should you proportion first or last?

first

q cold = - q hot

or

q_rxn = -q_water

in q = msΔT, what is specific heat measured in, and what is heat capacity measured in?

Specific heat = s, measured in J/gºC

heat capacity = ms, measured in J/ºC

what is q = nΔHº measured in?

kJ/mol

Heat at constant pressure is equal to?

q_v = ΔE

ΔH_fusion vs ΔH_vap

ΔH_{fusion = S → L}

ΔH_{vap = L → G}

What is enthalpy and what is it measured in

ΔH, in kj/mol

How to know if a reaction is endothermic or exothermic

q or ΔH > 0 , endothermic

q or ΔH < 0, exothermic

Heat of formation reaction

measured by ΔHºf

a reaction that MAKES ONE mole of substance from elements in their STANDARD states (they will have ΔHºf = 0 in chart)

What can you find using the (co)(products)-(co)(reactants) equation, and what are they measured in?

ΔHº, in kJ/ mol

ΔGº, in kJ/ mol

ΔSº, in J/mol K

Heat of combustion reaction

the breaking of 1 mol of substance into co2(g) and H₂O(l)

Heat of atomization reaction

ΔH_atom

BREAKING bonds in a molecule to produce ATOMS (singular: c, o, h) in the GAS phase.

Entropy, S, can be calculated how?

1. From phase change (s → l → gas)

2. from mols of GAS

• ΔS > 0 when mols of gas increase

• ΔS < 0 when mols of gas decrease

• ΔS = 0 when stays the same

3. ΔS = Q/T

In relation to entropy, when is a reaction favorable or not

ΔS > 0, favorable (more disorder)

ΔS < 0, unfavorable (less disorder)

How to know if a reaction moves forward, back, or in equillibrium?

K > Q and ΔG < 0 , reaction moves forward →

K < Q and ΔG > 0, reaction is reverse ←

K = Q and ΔG = 0 , reaction is in equillibrum

How to know if a reaction is extensive or not / prefers product or reactant

K > 1 and ΔGº < 0 , reaction is extensive and prefers product

K < 1 and ΔGº > 0, reaction is non extensive and prefers reactant

formula and rules for calculating Q and K

Q and K = (products)^coefficients/ (reactants)^coefficient

Only include aq and gas, no solids/liquids

for qrxn= - qwater problems, how should you proportion?

Proportion second with the CALCULATED number and divide it by the given number

J to kJ conversion

1 kJ = 1000 J

Bomb calorimetry equation

ΔE_comb = -CΔT

(c = heat capacity)

If a calorimeter is open to atmosphere, the heat is measured at ?

If a calorimter is in a closed container, the heat is measured at?

Open = ΔH, constant pressure

Closed, ΔE, constant volume

second ΔE formula for bomb calorimetry

ΔE = ΔH + -nRT in kJ/mol

use this formula after finding ΔE from ΔE = -CΔT