Chemistry 161 Chapter 6

Question

If 7.900 g C6H67.900 g C6⁢H6 is burned and the heat produced from the burning is added to 5691 g5691 g of water at 21 ∘21⁢ ∘C, what is the final temperature of the water?

Answer 1

You need the heat of combustion of benzene (3269 kJ/mole: Negative as a ΔH) or you can use ΔH_f°s and the combustion equation C₆H₆ + (9/2)O₂ → 6CO₂ + 3H₂O

ΔH_rxn = 3ΔH_{f,H2O(liq or g)} + 6ΔH_f,CO2 - ΔH_f,Benz This will be a different, though similar result because one is at combustion temperature and one is at 25°C.

The formula for the heat generated released as heat taken in by the water is

-n_BΔH_B,Comb = m_wc_w(T_f - T_i)

n_B = m_B/M_B where M_Benz = 78.11 g/mole

c_w = 4.184 J/g-K

and you know the enthalpy of combustion (express as -3269000 J/mole) and T_i: solve for T_f

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