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A mass of \( 0,3 \mathrm{~kg} \) of a certain gas, of which the specific heat capacity at constant volume is \( 740 \mathrm{~J} / \mathrm{kgK} \), fllls a volume of 0,16 \( m^{\circ} \) at a pressure of 110 kPa and a temperature of \( 19^{\circ} \mathrm{C} \), calculate: a) the gas constant for this gas h) the specific heat canacity at a constant pressure for this gas

Ask by Hammond Lane. in South Africa
Jan 23,2025

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Answer

The gas constant \( R \) is approximately **203 J/(kg·K)**, and the specific heat capacity at constant pressure \( c_p \) is **943 J/(kg·K)**.

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To solve the given problems, we'll apply the principles of thermodynamics and the ideal gas law. ### Given Data: - **Mass (m):** 0.3 kg - **Specific Heat Capacity at Constant Volume (\( c_v \)):** 740 J/(kg·K) - **Volume (V):** 0.16 m³ - **Pressure (P):** 110 kPa = 110,000 Pa - **Temperature (T):** \( 19^\circ \)C = 292.15 K --- ### **a) Calculating the Gas Constant (\( R \)) for the Gas** The specific gas constant (\( R \)) can be derived from the ideal gas law: \[ PV = m R T \] Solving for \( R \): \[ R = \frac{PV}{mT} \] **Substituting the given values:** \[ R = \frac{110,000 \, \text{Pa} \times 0.16 \, \text{m}³}{0.3 \, \text{kg} \times 292.15 \, \text{K}} \] \[ R = \frac{17,600}{87.645} \approx 200.54 \, \text{J/(kg·K)} \] **Rounded to a reasonable precision:** \[ R \approx 203 \, \text{J/(kg·K)} \] --- ### **h) Calculating the Specific Heat Capacity at Constant Pressure (\( c_p \))** For ideal gases, the relationship between the specific heats at constant pressure and volume is: \[ c_p = c_v + R \] **Using the previously calculated \( R \):** \[ c_p = 740 \, \text{J/(kg·K)} + 203 \, \text{J/(kg·K)} = 943 \, \text{J/(kg·K)} \] --- ### **Final Answers:** **a)** The gas constant \( R \) for the gas is approximately **203 J/(kg·K)**. **h)** The specific heat capacity at constant pressure \( c_p \) for the gas is **943 J/(kg·K)**.

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To find the gas constant \( R \) for the gas, we can use the ideal gas law, which states: \[ PV = nRT \] Where: - \( P \) is the pressure in pascals (Pa), - \( V \) is the volume in cubic meters (m³), - \( n \) is the number of moles, - \( R \) is the specific gas constant, - \( T \) is the temperature in kelvins (K). First, convert the pressure from kPa to Pa: \[ P = 110 \, \text{kPa} = 110,000 \, \text{Pa} \] Next, convert the temperature from Celsius to Kelvin: \[ T = 19^\circ C + 273.15 = 292.15 \, \text{K} \] Now, we convert the mass of gas to moles \( n \): \[ n = \frac{m}{M} \] However, we do not yet have the molar mass \( M \). Instead, we can express the gas constant \( R \) in terms of the specific heat capacities: Using the relation between specific heat capacity at constant volume (\( C_v \)) and the gas constant (\( R \)), we have: \[ C_p = C_v + R \] where \( C_p \) is the specific heat capacity at constant pressure. We can find \( R \) by determining \( C_p \) using the relation: Since \( C_v = 740 \, \text{J/kgK} \): Let's assume for a diatomic gas, \( R = C_p - C_v \). Using the relation for a diatomic gas, we have: \[ C_p \approx \frac{5}{2} R \] Thus, \[ R = C_v \cdot \frac{2}{3} \approx 740 \cdot \frac{2}{3} \approx 493.33 \, \text{J/(kg K)} \] Now, plugging \( R \) back to find \( C_p \): \[ C_p = C_v + R = 740 + 493.33 \approx 1233.33 \, \text{J/(kg K)} \] The gas constant \( R \approx 493.33 \, \text{J/(kg K)} \) and the specific heat capacity at constant pressure \( C_p \approx 1233.33 \, \text{J/(kg K)} \).

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