The values of ΔH for the combustion of ethene and ethyne are -341.1 and -310.0 K cal respectively. Which of the following is a better fuel:a)C2H2b)C2H4c)Both a and b d)None of theseCorrect answer is option 'A'. Can you explain this answer?

Question

The values of &#916;H for the combustion of ethene and ethyne are -341.1 and -310.0 K cal respectively. Which of the following is a better fuel:a)C2H2b)C2H4c)Both a and b       d)None of theseCorrect answer is option 'A'. Can you explain this answer?

Answer

Zero Standard Molar Enthalpy of Formation at 298 K

Standard molar enthalpy of formation (∆Hf°) is the energy change that occurs when one mole of a compound is formed from its constituent elements in their standard states under standard conditions of temperature and pressure (298 K and 1 atm).

The species which has a zero standard molar enthalpy of formation means that the energy change that occurs when one mole of the compound is formed from its constituent elements is zero. This can happen only if the compound is an element itself.

Answer Explanation

Among the given options, Cl2(g) is the species which has zero standard molar enthalpy of formation at 298 K.

When one mole of Cl2(g) is formed from its constituent elements Cl(g), the energy change involved is zero at 298 K. This is because Cl2(g) is an element itself and its formation from Cl(g) requires no energy input or release.

On the other hand, Br2(g), H2O(g), and CH4(g) are compounds and their formation from their constituent elements requires energy input or release. Hence, their standard molar enthalpy of formation is not zero.

Therefore, the correct answer is option 'B' (Cl2(g)).

Answer

Explanation:
Standard molar enthalpy of formation (ΔHf°) is the enthalpy change when one mole of a compound is formed from its constituent elements in their standard states, under standard conditions of 298 K and 1 atm pressure.

The standard state of an element is the most stable form of the element at 298 K and 1 atm pressure. For example, the standard state of chlorine is Cl2(g) and not Cl(g) or Cl-(aq).

The enthalpy change for the formation of an element from its standard state is zero by definition. For example, the enthalpy change for the formation of Cl2(g) from its standard state (Cl2(g)) is zero.

Therefore, the species which by definition has ZERO standard molar enthalpy of formation at 298 K is an element in its standard state.

Out of the given options, the only species which is an element in its standard state is Cl2(g).
Hence, the correct answer is option 'B'.

Answer

Answer

I think ans should be b part

Answer

Ethene is the right answer. because more is the calorific  value more is power of fuel.  here it is higher  for ethene

Answer

All elements in their standard states have a standard enthalpy of formation of zero kilo joules per mole.

Chlorine exists as a gas at room temperature.

The standard enthalpy of formation of chlorine gas is ∆fH^0=0kJmol-1 as the element is already in its standard states.

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