An ideal gas expands while the pressure is kept constant. During the process, does heat flow into the gas or out of the gas? Justify you answer.

Explanation

To determine whether heat flows into or out of an ideal gas during an expansion at constant pressure, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Ideal Gas Law**: The ideal gas law is given by the equation \( PV = nRT \), where \( P \) is pressure, \( V \) is volume, \( n \) is the number of moles, \( R \) is the universal gas constant, and \( T \) is temperature.

2. **Identify the Process**: In this scenario, the gas is expanding at constant pressure. This means that \( P \) remains unchanged while \( V \) (volume) increases.

3. **Relate Volume and Temperature**: According to the ideal gas law, if pressure is constant and volume increases, the temperature must also increase. This can be expressed as:
\[ V \propto T \quad \text{(at constant P)} \]
Therefore, if \( V \) increases, \( T \) must also increase.

4. **Determine the Change in Temperature**: Since the volume is increasing, the change in temperature \( \Delta T \) is positive:
\[ \Delta T > 0 \]

5. **Calculate Heat Transfer**: In a constant pressure process, the heat transferred \( Q \) can be calculated using the formula:
\[ Q = nC_p \Delta T \]
where \( C_p \) is the specific heat capacity at constant pressure. Since \( n \) (number of moles) and \( C_p \) are positive constants, and \( \Delta T \) is also positive, we conclude that:
\[ Q > 0 \]

6. **Conclusion**: A positive value of \( Q \) indicates that heat flows into the gas during the expansion process. Therefore, heat flows into the gas.

### Final Answer:
During the expansion of an ideal gas at constant pressure, heat flows into the gas.

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