Enthalpy Change?

Question

What is the enthalpy change when 22.5 g of CH4 are burned in excess O2?
CH4(g) + 2O2(g) ------>CO2(g) + 2H2O(l) DH°= -890 kJ

A. -39.5 kJ
B. -890 kJ
C. -1250 kJ
D. +890 kJ
E. +1250 kJ
no need to solve, How do you know?

Answer 1

Do the calculation in moles!!
Molar mass of CH4: 16
22.5 g of CH4 <==> 1.41 mole CH4
ΔH°= -890 kJ/mol <==> ΔH = -1.25x10^3 kJ/mol for burning 1.41 mole CH4
ANSWER: C.