The heat of combustion of ethanol into carbon dioxide and water is –327 kcal at constant pressure. The heat evolved (in cal) at constant volume and `27^(@)C` (if all gases behave ideally) is (R = 2 cal `mol^(–1) K^(–1)` __________.

Explanation

To solve the problem step by step, we need to find the heat evolved at constant volume (ΔU) from the given heat of combustion at constant pressure (ΔH). Here's how to approach the solution:

### Step 1: Write the combustion reaction of ethanol
The combustion of ethanol (C2H5OH) can be represented as:
\[ \text{C}_2\text{H}_5\text{OH (l)} + 3 \text{O}_2\text{(g)} \rightarrow 2 \text{CO}_2\text{(g)} + 3 \text{H}_2\text{O (l)} \]

### Step 2: Identify the values given
- The heat of combustion (ΔH) at constant pressure is given as -327 kcal.
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