Standard enthalpy of vaporization for is . Heat required for vaporization of of at constant temperature is:
- A
- B
- C
- D
Standard enthalpy of vaporization for is . Heat required for vaporization of of at constant temperature is:
Correct answer:A
Standard Method
Given: Standard enthalpy of vaporization of is and mass of is .
Find: Heat required for vaporization of of .
First, calculate the molar mass of :
Now calculate the number of moles:
Use the relation:
So,
On rounding, the heat required is . Therefore, the correct option is A.
Direct Proportionality Method
Given: mole of requires for vaporization.
Find: Heat required for of .
Since molar mass of is , the required heat is directly proportional to mass:
Therefore, the required heat is approximately , so the correct option is A.
Using the given mass directly in the enthalpy formula is incorrect because is given per mole, not per gram. First convert into moles, then multiply by .
Calculating the molar mass of incorrectly leads to the wrong answer. Do not forget that there are chlorine atoms, so the molar mass is .
Confusing vaporization enthalpy with some other thermodynamic quantity is wrong because the question specifically asks for heat required for vaporization at constant temperature. Use standard enthalpy of vaporization, not combustion or formation enthalpy.
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