CH302H - Principles of Chemistry II: Honors
Spring 2016, Unique 494200

Homework, Week 2


Homework, week 2
Answer key

1. Calculate the molar entropy of a constant-volume sample of neon at 500 K given that it is 146.22 J K-1 mol-1 at 298 K and CV,m = 3/2R.

2.  Determine DS (for the system) when 3.0 mol of an ideal gas at 25˚C and 1.0 atm is heated to 125˚C and expanded to 5.0 atm.  Rationalize the sign of DS. CV,m = 3/2R, CP,m = 5/2R.

3.  Consider a system containing 2.0 mol CO2(g) (Cv,m = 28.8 J K-1 mol-1), initially at 25˚C and 10 atm and confined to a cylinder of cross-section 10.0 cm2.  It is allowed to expand adiabatically against a constant external pressure of 1.0 atm until the piston has moved outwards through 20 cm.  Determine q, w, DU, DH, and DS. 

4.  Determine the standard reaction entropy at 298 K of the following reactions:

a) 2 CH3CHO(g) + O2(g) --> 2 CH3COOH(l)

b) Hg(l) + Cl2(g) --> HgCl2(s)

5.  A 500 g block of copper (Cp,m = 24.4 J K-1 mol-1) initially at 293 K is in thermal equilibrium with an electric heater of resistance 1.0 kW and negligible mass.  A current of 1.0 A is passed for 15.0 s.  Determine the change in entropy of the copper block.  The experiment is then repeated with the copper immersed in a stream of water that maintains its temperature at 293 K.  Determine the change in entropy of the copper and the water.

6.  4.0 moles of an ideal gas is divided evenly in a cylinder separated into 2 chambers, A and B, that are partitioned with a movable insulating boundary.  Initially, the volume and temperature of both chambers is 2.0 L and 300 K, respectively.  Each chamber has an independent heater that is used to supply heat.  The heater for chamber B is used to maintain the temperature of B at all times.  The heater for chamber A is used to supply heat to chamber A to move the boundary between A and B reversibly to decrease the volume of chamber B by half.  Determine DH for each chamber, assuming CV,m = 20 J K-1 mol-1.

7.  For each of the following processes determine whether DSsys is greater than zero, less than zero, or equal to zero.  Explain your reasoning.

a) A process in which no heat is exchanged between system and surroundings.

b) An isothermal expansion of an ideal gas.

c) An isobaric (i.e. constant pressure) cooling of an ideal gas.

d) Isobaric evaporation of a liquid. 

8.  Vaporization at the normal boiling point of a substance (the boiling point at 1 atm, Tvap) is a reversible process.  If DHvap of water is 40.65 kJ mol-1, determine DSvap when 2.0 moles of water are vaporized at 100˚C.  Comment on the sign of DSvap.