During an adiabatic expansion the temperature of 0.600mol of oxygen drops from 30°C to 10°C.

1.How much work does the gas do?

2.How much heat is added to the gas?

1 answer

To analyze the adiabatic expansion of the gas, we need to apply the relevant thermodynamic principles.

  1. Work Done by the Gas (W):

For an adiabatic process, the work done by the gas can be calculated using the first law of thermodynamics, which states:

\[ \Delta U = Q - W \]

Where:

  • \(\Delta U\) is the change in internal energy.
  • \(Q\) is the heat added to the system (which is 0 for an adiabatic process).
  • \(W\) is the work done by the system.

Since the process is adiabatic, \(Q = 0\), so the equation simplifies to:

\[ \Delta U = -W \]

To find the change in internal energy, we use the formula:

\[ \Delta U = nC_v \Delta T \]

Where:

  • \(n\) is the number of moles (0.600 mol).
  • \(C_v\) is the molar heat capacity at constant volume (for diatomic gases like O2, \(C_v \approx 5/2 R\) where \(R = 8.314 , \text{J/(mol·K)}\)).
  • \(\Delta T\) is the change in temperature.

First, let's convert the temperatures from Celsius to Kelvin:

  • \(T_i = 30°C = 303.15 , K\)
  • \(T_f = 10°C = 283.15 , K\)

Now, calculate \(\Delta T\):

\[ \Delta T = T_f - T_i = 283.15 , K - 303.15 , K = -20 , K \]

Now, we calculate \(\Delta U\):

\[ C_v = \frac{5}{2} R = \frac{5}{2} \times 8.314 , \text{J/(mol·K)} \approx 20.786 , \text{J/(mol·K)} \]

\[ \Delta U = nC_v \Delta T = 0.600 , \text{mol} \times 20.786 , \text{J/(mol·K)} \times (-20 , K) \]

Calculating \(\Delta U\):

\[ \Delta U = 0.600 \times 20.786 \times (-20) \approx -249.432, \text{J} \]

Since \(\Delta U = -W\):

\[ W = -\Delta U = 249.432, \text{J} \]

Thus, the work done by the gas is approximately:

\[ W \approx 249.43 , \text{J} \]

  1. Heat Added to the Gas (Q):

As already established, for an adiabatic process, no heat is added or removed from the system:

\[ Q = 0 , \text{J} \]

Summary:

  1. The work done by the gas is approximately 249.43 J.
  2. The heat added to the gas is 0 J (since the process is adiabatic).