For an ideal gas, constant-pressure and constant-volume specific heats differ by the specific gas constant.
Difficulty
Intermediate
Read time
4 min
Prerequisites
Consistent SI units, algebra, and the physical assumptions listed below
Source
Teng-Jui Lin — Equation SheetsAdapted from Teng-Jui Lin, Equation Sheets — Mechanical Engineering, under CC BY 4.0.
Adapted notation and added original explanations, variables, assumptions, applications, and a worked example. Converted the source's molar-basis relation to a consistent mass basis.
For an ideal gas, constant-pressure and constant-volume specific heats differ by the specific gas constant. Use either a mass basis throughout or a molar basis throughout; mixing the universal gas constant with mass-specific heat capacities gives incorrect units.
| Symbol | Meaning | Units |
|---|---|---|
| Mass-specific heat at constant pressure | ||
| Mass-specific heat at constant volume | ||
| Specific gas constant |
Recover c_v from c_p and a known specific gas constant.
Keep ideal-gas heat-capacity data on a consistent basis.
An ideal-gas model uses c_p = 1005 J/(kg·K) and R_s = 287 J/(kg·K). Find c_v.
Adapted from Teng-Jui Lin, Equation Sheets — Mechanical Engineering, under CC BY 4.0.
Adapted notation and added original explanations, variables, assumptions, applications, and a worked example. Converted the source's molar-basis relation to a consistent mass basis.
Assumptions
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