Question

2) Construct a table (or use the one below) with 9,w, AU, AH as the headings. Determine whether each of these quantities is postive, negative, or zero for five (5) of the following nine processes. (If you choose more than five, only the first five answers will be graded, so decide which five you are most confident in and only answer those.) (4 pts each. 20 pts total) 1. Freezing of acetone at 1 atm and it's normal freezing point. b. An irreversible, isothermal expansion of an ideal gas. c. An adiabatic compression of an ideal gas. d. The reaction of sodium with water. e. Boiling liquid ammonia at its normal boiling point. f. Irreversible, adiabatic expansion of a gas against an external pressure. g Reversible, isothermal compression of an ideal gas. h. Heating a gas at constant volume. i. Freezing water at its normal freezing point 9 w AU AH a b с d e f 8 h

Answer 1

An irreversible isothermal expansion of an ideal gas:
In any isothermal process, temperature remains constant. Hence,

Q1: $\Delta$ U = n c_v$\Delta$T = 0 and

Q2: $\Delta$ H = nc_P$\Delta$T = 0
Q3: Workdone, W = P_ext * (V_f –V_i) where, P_ext = external force, V_f = final volume and V_i = initial volume.

It is an expansion work. Therefore, V_f > V_i. Hence, (V_f –V_i) >0.

Again P_ext >0
Therefore, W = (+)value.

Q4: According to first law of thermodynamics,
$\Delta$ U = W + Q
As, U = 0, Q = -W = (-)value (as W is a + value).

Q	W	$\Delta$U	$\Delta$H
negative	positive	0	0