The heat of combustion of ethanol into carbon dioxide and water is at constant pressure. The heat evolved (in cal) at constant volume at is .

[; Assume all gases behave ideally]

Question

The heat of combustion of ethanol into carbon dioxide and water is  at constant pressure. The heat evolved (in cal) at constant volume at  is .

[; Assume all gases behave ideally]

Canvas Classes · Accepted Answer

Strategy:
 Use the relation between enthalpy change () at constant pressure and internal energy change () at constant volume: . Recall that only gaseous species contribute to .

Step 1: Write the combustion equation

Step 2: Calculate

.

Step 3: Solve for 
Given: .
Given: .

.
The magnitude of heat evolved at constant volume is .

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