Question 88 of 949
A gas with initial volume of 2 X 10\(^{-6}m^3\) is allowed to expand to six times its initial value at constant pressure of 2 x 10\(^5Nm^{-2}\). The work done is?
- A. 2.0J
- B. 4. 0 J
- C. 12.0 J
- D. 2.4 J
Correct Answer:
A
Explanation
To solve the problem of calculating the work done by a gas during expansion at constant pressure, we can use the formula for work done in a thermodynamic process:
### Formula for Work Done
The work done \( W \) by a gas during expansion at constant pressure is given by the formula:
\[
W = P \Delta V
\]
where:
- \( W \) is the work done (in joules, J),
- \( P \) is the constant pressure (in pascals, Pa),
- \( \Delta V \) is the change in volume (in cubic meters, m³).
### Step-by-Step Solution
1. **Identify the Initial Volume**:
The initial volume \( V_i \) of the gas is given as:
\[
V_i = 2 \times 10^{-6} \, m^3
\]
2. **Calculate the Final Volume**:
The gas expands to six times its initial volume. Therefore, the final volume \( V_f \) is:
\[
V_f = 6 \times V_i = 6 \times (2 \times 10^{-6}) = 12 \times 10^{-6} \, m^3
\]
3. **Calculate the Change in Volume**:
The change in volume \( \Delta V \) is calculated as:
\[
\Delta V = V_f - V_i = (12 \times 10^{-6}) - (2 \times 10^{-6}) = 10 \times 10^{-6} \, m^3
\]
4. **Identify the Constant Pressure**:
The constant pressure \( P \) is given as:
\[
P = 2 \times 10^5 \, N/m^2
\]
5. **Calculate the Work Done**:
Now, substituting the values of \( P \) and \( \Delta V \) into the work done formula:
\[
W = P \Delta V = (2 \times 10^5) \times (10 \times 10^{-6})
\]
\[
W = 2 \times 10^5 \times 10 \times 10^{-6} = 2 \times 10^5 \times 10^{-5} = 2 \times 10^0 = 2 \, J
\]
### Conclusion
The work done by the gas during its expansion at constant pressure is:
\[
\boxed{2.0 \, J}
\]
### Explanation of Other Options
- **Option B (4.0 J)**: This option is incorrect because it likely results from a miscalculation of either the change in volume or the multiplication with pressure.
- **Option C (12.0 J)**: This option is incorrect as it may stem from misunderstanding the relationship between pressure and volume change, possibly assuming a different process or misapplying the formula.
- **Option D (2.4 J)**: This option is also incorrect, possibly due to an error in calculating the change in volume or misapplying the pressure value.
### Common Pitfalls
- **Misunderstanding the Process**: Remember that the work done formula applies specifically to processes at constant pressure.
- **Volume Units**: Ensure that all volume measurements are in cubic meters when using SI units.
- **Pressure Units**: Always check that pressure is in pascals (N/m²) for consistency in calculations.
### Revision Summary
- Work done by a gas at constant pressure is calculated using \( W = P \Delta V \).
- Ensure to calculate the change in volume correctly by subtracting initial volume from final volume.
- Always use consistent units (SI units) for pressure and volume.
- Double-check calculations to avoid common errors in thermodynamic problems.