The complete combustion of acetic acid

Question

I had a lot of trouble doing this and research online didn't help me much either. This is similar to what my homework is-

The complete combustion of acetic acid, HC2H302 to form H2O and CO2 at constant pressure releases 871.7kJ of heat per mole of HC2H302 

I am supposed to :

a. Write a balanced equation. 

b. How much heat is released from the combustion of 12.0g of HC2H3O2 with excess oxygen gas? 

(I ended up getting -163.23kJ but i am not sure if this is correct)

c. How many grams of HC2H3O2( are needed to produce 560kJ? 

Answer 1

a.) CH3COOH + 2O2 ==> 2CO2 + 2H2O

b.) 871.7 kJ/mole x 1 mol/60.05 g x 12.0 g = 174.2 kJ = 174 kJ (3 sig. figs.) Since it asks how much heat is RELEASED, you don't necessarily need the minus sign.

c.) 560 kJ x 1 mole/871.7 kJ x 60.05 g/mole = 38.6 g = 38 g (2 sig. figs.)