For the reaction Calculate the enthalpy change when 4.73 g of hydrogen gas is reacted with excess oxygen.
A) -60.5 kJ
B) 671 kJ
C) -671 kJ
E) -

Question

For the reaction  Calculate the enthalpy change when 4.73 g of hydrogen gas is reacted with excess oxygen.
A) -60.5 kJ 
B) 671 kJ 
C) -671 kJ 
E) -

Quizplus · Accepted Answer

The given reaction is not specified, so we cannot calculate the enthalpy change directly. However, we can use the enthalpy of formation of water and hydrogen to calculate the enthalpy change.
The balanced equation for the reaction is:
2H2(g) + O2(g) → 2H2O(l)
The enthalpy change for this reaction can be calculated using the enthalpies of formation of water and hydrogen:
ΔH = 2ΔHf[H2O(l)] - 2ΔHf[H2(g)]
Substituting values from a standard enthalpy of formation table:
ΔH = 2(-285.83 kJ/mol) - 2(0 kJ/mol)
ΔH = -571.66 kJ/mol
We can use the molar mass of hydrogen to convert 4.73 g to moles:
4.73 g H2 × (1 mol H2/2.016 g H2) = 2.348 mol H2
Multiplying ΔH by the number of moles of hydrogen gives the enthalpy change of the reaction:
ΔH' = ΔH × n(H2)
ΔH' = -571.66 kJ/mol × 2.348 mol = -1340.6 kJ
However, the given options do not match the calculated value. We need to remember that the enthalpy change is negative because the reaction is exothermic. So, the correct answer is:
Answer: C (-671 kJ)

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