# 4 very hard thermodynamics problems

1. Oct 17, 2010

### osprey099

1. Suppose a piece of solid bismuth weighing 27.7 g at a temperature of 253 °C is placed in 277 g of liquid bismuth at a temperature of 333 °C. Calculate the temperature after thermal equilibrium is reached, assuming no heat loss to the surroundings. The enthalpy of fusion of solid bismuth is ΔHfus = 11.0 kJ mol–1 at its melting point of 271 °C, and the molar heat capacities CP of solid and liquid bismuth are 26.3 and 31.6 J K–1 mol–1, respectively.

2. The standard enthalpy change of combustion [to CO2(g) and H2O()] at 25°C of the organic solid decanoic acid, C10H20O2(s), is determined to be -6060.3 kJ mol–1. What is the Hf° of C10H20O2(s) based on this value?

Use the following data: Hf° H2O () = -285.83 kJ mol-1 ; Hf° CO2(g) = -393.51 kJ mol-1

3. If 52.3 g of argon at 351 K is compressed isothermally and reversibly from a pressure of 1.97 atm to 4.37 atm, calculate the work done on the gas and the heat absorbed by the gas in the process. What are the changes in energy (ΔU) and in enthalpy (ΔH) of the gas?

4. When 2.42 g of copper(II) chloride (CuCl2) is dissolved in 106 g of water in a Styrofoam calorimeter of negligible heat capacity, the temperature increases from 25.00 to 27.09 °C. Based on this observation, calculate q for the water and ΔH° for the process.
CuCl2(s) Cu2+(aq) + 2Cl- (aq)
The specific heat of water is 4.184 J K–1 g–1.

Please explain how you solved them i have no idea where to start. thermo is my worst nightmare

2. Oct 18, 2010

### Astronuc

Staff Emeritus
Start with demonstrating some effort please.

One needs to be familiar with phase change, e.g., when solid melts to liquid, or liquid freezes to solid, which occurs at the melting point.

Ostensibly classroom instruction and one's text book would provide the basic theory to help one get started on these problems.

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