Monday 13 October 2014 Read: –Section 3.3. Problems: –3.16, 3.18, 3.22, 3.36.

Sample Problem 2.00 mole of Nitrogen at 1.00 atm, 25°C is allowed to Expand isothermally to final pressure of atm. Calculate work done if the expansion is carried out a.) against a vacuum b.) against a constant external pressure of atm c.) reversibly

Solution: a.) against a vacuum P ex = 0 (no weight) w = -P ex ΔV = 0 No work! 4

Solution: b.) against a constant external pressure of atm Work will be done in expansion on surroundings 5

Solution: c.) reversible expansion Work will be done in expansion on surroundings 6

Total Energy And Internal Energy Translational Energy Rotational Energy Vibrational Energy Electronic Energy Chemical Energy h Total Energy Internal Energy ? ? PE = m g h KE = ? h KE = ½ mv 2 > 0 PE = m g h

HEAT is NOT Energy BUT Transfer of Energy 3 3 Energy of isolated system is conserved E1E1 E1E1 E2E2 E2E2 E = E 1 + E 2 = C ΔE = C – C = 0 E = E 1 + E 2 = C ΔE = C – C = 0 -q 1 +q 2 E = E 1 + (-q 1 ) + E 2 + (+q 2 ) = C ∑q i = 0 E 1 E 2 ? ? E = E 1 + E 2 + (-q 1 ) + (+q 2 ) = C (-q 1 ) + (+q 2 ) = ? ? ? 25 o C 70 o C 25 o C 100 o C 25 o C 70 o C

Exothermic Endothermic HEAT is NOT a State Function K 200 K ΔE in 0 ? ? 200 K 100 K ΔE in 0 ? ? Initial State Final State q > 0 q = 0

How do we measure HEAT transfer (q)? Using constant-volume adiabatic bomb Calorimeter 4 4

Sample Problem g of nickel at 150.° C was placed in 1.00 L of water at 25.0° C. What is the final temperature of the water after thermo- equilibrium has been established. Assume this is an isolated system and heat is only transferred between nickel and water (not to surroundings). The specific heat capacity of nickel is J·g - 1 ·C -1.

Solution: 1 cal = J exactly 1 cal = energy needed to raise 1 g of water by 1° from 14.5° to 15.5°C Heat lost by nickel = heat gained by water -q Ni = q water 12

First law of thermodynamics 5 5 Under Constant Pressure ex. Lab bench Under Constant Pressure ex. Lab bench Under Constant Volume ex. Bomb Calorimeter Under Constant Volume ex. Bomb Calorimeter Irreversible gas expansion

Enthalpy, a new State Function 5 5 Under Constant Pressure ex. Lab bench Under Constant Pressure ex. Lab bench Under Constant Volume ex. Bomb Calorimeter Under Constant Volume ex. Bomb Calorimeter qpqp qpqp -w qvqv qvqv ΔU ΔH ? ? If gas expands qvqv qvqv -w qpqp qpqp If gas compresses

Sample Problem g of Naphthalene (C 10 H 8, MW=128.2 g/mol) was “combusted” in a constant-volume calorimeter (C V = J·K -1 ), where the water temperature increased from 20.17° to 24.08°C. Calculate the molar ΔH and ΔU 20.17°C) for the combustion (oxidation) of Naphthalene (units: kJ·mole -1 ).