Question

The thermochemical equation for the combustion (i.e., burning) of one mole of benzene under standard conditions is

C6H6(l)+15/2O2(g)→6CO2(g)+3H2O(l)

with ΔHocomb=–3267.7kJ/mol

1. Is this reaction exothermic or endothermic?
2. How much heat is released when a 5.00-g sample of benzene is burned in excess oxygen under standard conditions? (m.w. C₆H₆ = 78.11 u)

Answer 1

1)

Since ΔH is negative, the reaction is exothermic

Answer: exothermic

2)

mass(C6H6)= 5.00 g

use:

number of mol of C6H6,

n = mass of C6H6/molar mass of C6H6

=(5 g)/(78.11 g/mol)

= 6.401*10^-2 mol

Now use:

Q = number of mol * ΔH

= (6.401*10^-2 mol) * (-3267.7 KJ/mol)

= -209.2 KJ

So,

209.2 KJ is heat released

Answer: 209.2 KJ