Question

The heat of combustion of methane is ΔHcomb = -890 kJ/mol. How

much heat is released when 4.40 g of methane is burned at constant
pressure?

Answer 1

-245 kJ with 3 sig figs

Step-by-step explanation:

The heat of combustion of methane (CH4) of -890 kJ/mol tells us that 890,000 Joules (energy) is released (the negative sign means released) for every 1 mole of methane combusted.

We are given 4.40 grams of methane to combust. We need to find how many moles of methane this represents. The molar mass of methane is 16.0 grams/mole. The moles is determined by dividing the given mass by the molar mass:

(4.40 grams)/(16.0 grams/mole) = 0.275 moles CH4

Now we can calculate the energy released:

(0.275 moles CH4)*(-890 kJ/mole) = -245 kJ with 3 sig figs

[Note that moles cancel and kJ moves to the top]