Hello, James,
Were you given a heat of enthalpy for C6H6? We need to know how much energy is available in order to answer the question. I looked up what I think is a representative value: -3301 kJ/mole. The minus sign indicates heat is released in combustion.
8.7 grams of benzene is 0.1115 moles. The energy released in combustion of this amount is:
(-3301 kj/mole)*(0.1115 moles) = -368.2 kJ
That amount of heat is transferred to 5691 g of water. Water's specific heat is 4.8 J/gC. The equation for finding the temperature change is:
q = mcDT,
where q is the heat (in Joules), m is the amount, c is the specific heat of water, and DT is the temperature change.
The heat from the combustion is absorbed by the water, so it is the positive value of the heat of combustion. It needs to be in Joules (not kJ) so we'll convert it.
368200 J = (5691g)*(4.8 J/gC)*(T2 - 21C)
T2 = 34.5 C
Bob
