What would ∆H be for the reaction 9 A + 3 B → 6 C?

Question

Consider the hypothetical thermochemical equation 3 A + B → 2 C for which ΔH = 65.5 kJ/mol.

a)If you have 5.30 moles of A, how much heat would be absorbed?

b)If the reaction absorbs 345 kJ of heat, how many moles of C would be produced?

c)What would ∆H be for the reaction 2 C → 3 A + B?

d)What would ∆H be for the reaction 9 A + 3 B → 6 C?

Answer 1

3A + B ==> 2C ... ∆H = 65.5 kJ/mol

a) 5.30 mol A x 65.5 kJ/3 mol A = 116 kJ

b) 345 kJ x 2 mol C/65.5 kJ = 10.5 moles C

c) 2C ==> 3A + B is the reverse of the given reaction, therefore ∆H = -65.5 kJ/mol

d) 9A + 3B ==> 6C is 3x the original reaction, therefore ∆H = 3 x 65.5 = 197 kJ