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Chemistry 2301

Fall 2022

Assignment 3

1. (10 points total)

a. (5 points) The heat of combustion of ethanol is 1367 kJ/mol. Calculate the energy released as heat when a 10 g of ethanol is burned in air.

b. (5 points)  The heat capacity of water at room temperature and constant pressure is  75 J/molK. Estimate how high in temperature one liter of water could be heated from room temperature by burning 10 g of ethanol, assuming the heat capacity of water is constant.

2. (20 points) One mole of an ideal gas, initially at 0°C and 1 atm pressure, and having a heat capacity of C¯v = 21 J/molK, is put through the following reversible cycle:

Step 1: heat at constant volume to double the initial pressure.

Step 2: expand adiabatically until the system returns to its initial temperature. Step 3: compress isothermally back to its initial state.

Calculate q, w, ΔU and ΔH for each step and for the entire cycle.

3. (40 points) Three systems each contain one mole of an ideal monatomic gas at 2 bar pressure and 25°C. Each system is doubled in volume by following one of three paths (all paths are reversible):

a. isothermal expansion

b. adiabatic expansion

c. expansion along a path described by the equation: p = 0.1V/n + b, where p is the internal pressure of the gas in bar, V is the volume in liters, n is the number of moles of gas and b is a constant whose value can be determined by the initial conditions.

Calculate the final pressure, ΔU, and w and make a plot of p vs V for each path (all plots can be overlaid on one graph).

4. (15 points) The sublimation temperature of solid CO2 is -78.5°C at 1 bar pressure. At what minimum pressure must CO2(g) be stored in a fire extinguisher at 25°C such that "snow" (solid CO2) is produced when the gas is released to atmospheric (~1 bar) pressure? Assume that the process is isenthalpic and that μJT = 1.1 K/bar and is constant with pressure and temperature (in reality it isn't, this is an approximation).

5. (15 points) The specific heat capacity of aluminum is 0.897 J/gK at constant pressure and 298K. Assuming the heat capacity of aluminum is constant with temperature, calculate q, w, ΔU and ΔH for a process in which 1 kg of aluminum is heated from 0°C to 100°C.