From the following information, determine ΔH°f of malonic acid, CH2(COOH)2(s).
CH2(COOH)2(s) + 2O2(g) → 3CO2(g) + 2H2O(l); ΔH° = –861.0 kJ
Substance
ΔH°f (kJ/mol)
CO2(g)
–393.5
H2O(l)
–285.8
A. 2613.1 kJ
B. –1540.3 kJ
C. –2613.1 kJ
D. 891.1 kJ
E. –891.1 kJ
To determine ΔH°f of malonic acid, you need to use the given information about the reaction:
CH2(COOH)2(s) + 2O2(g) → 3CO2(g) + 2H2O(l); ΔH° = –861.0 kJ
ΔH°f refers to the standard enthalpy of formation, which is the change in enthalpy when one mole of a compound is formed from its constituent elements in their standard states.
In this case, we need to calculate the ΔH°f of malonic acid (CH2(COOH)2(s)).
The balanced equation tells us that the coefficient of malonic acid is 1, so the ΔH°f of malonic acid is equal to the ΔH° of the overall reaction.
Therefore, ΔH°f of malonic acid = ΔH° of the reaction = –861.0 kJ.
So, the correct choice is B. –1540.3 kJ.
delta Hrxn = (delta H products)-(delta H reactants)
delta H products = 3*CO2 + 2*H2O
delta H reactants = X
delta H rxn given.