CHM 2045C Module Seven Sample Exam

Module Seven Part C: Specific Heat/First Law Problems 10 points

If the temperature of a 50.0 gram block of aluminum increases by 10.9 K when heated by 500 joules, calculate the: (See section 6.2 pages 241-246)

1. heat capacity of the aluminum block.

q = heat transferred C = specific heat capacity

m = mass of substance

ΔT = change in K temperature

Heat capacity of Block = q / Δ T

Heat Capacity of Block = 500 J / 10.9 K = 45.9 J/K

2. molar heat capacity of aluminum. Moles = Mass / Molar Mass

Moles = 50.0 g / 27.0 g/mol = 1.85 mol

Molar heat capacity = q / Δ T mol

Molar Heat Capacity = 500 J / 10.9 K 1.85 mol = 24.8 J/K mol

3. specific heat capacity of aluminum.

q = C x m x Δ T

500 J = C x 50.0 g x 10.9 K C = 0.917 J/gK

If the internal energy of a thermodynamic system is decreased by 300 J when 75 J of work is done on the system, how much heat was transferred, and in which direction, to or from the system. See section 6.4 p 253

Change Sign Conversion Effect of E_system

Work done on the system by surroundings w > 0 (+) E increases

Work done by the system on surroundings w < 0 (-) E decreases

Heat transferred to system from surroundings q > 0 (+) E increases

Heat transferred from system to surroundings q < 0 (-) E decreases

Δ E = q + w

Given Δ E= - 300 J w = + 75 J

- 300J = q + (+75J)

q = - 375 J of heat was transferred from the system to the surroundings