A triatomic molecule can be modelled as three rigid sphere joined by three rigid rods forming an triangle. Consider a triatomic gas consisting such molecule. If gas performs 30 J work when it expands under constant pressure the heat given to gas is:
Correct answer: D. 120 J
- A. 60 J
- B. 30 J
- C. 45 J
- D. 120 J
Explanation
The correct answer is 120 J. In thermodynamics, when a triatomic gas expands under constant pressure, the heat supplied to the gas (Q) is related to the work done (W) by the equation Q = nC_p∆T, where C_p for a triatomic gas is 4R. Therefore, Q = 4W. Given that the work done by the gas is 30 J, the heat added is Q = 4 × 30 = 120 J. This is why option D is correct, while the other options (A, B, and C) do not accurately represent the relationship and calculations involved.
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About Molar Specific Heat of a Gas
Molar specific heat is the heat required to raise the temperature of one mole of a gas by one kelvin, expressed through Q = nCΔT. Questions compare the constant volume value Cv with the constant pressure value Cp, apply the ideal gas relation Cp − Cv = R, and identify how the thermodynamic process affects heat capacity.
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