The decomposition of liquid benzene, C6H6, to gaseous acetylene, C2H2: C6H6 (l) 3 C2H2 (g) Delta H is 630 What is the total energy change of the system if 34.5 g of benzene decomposes at STP?

Answer 1

C6H6(l) →3C2H2 (g)...... ΔH=+630 kJ

34.5g C6H6 = ? kJ

Convert g C6H6 to moles with molar mass

1 mol C6H6 = 78.114 g C6H6

mol = grams / molarmass

mol=34.5/78.114

=0.441662 mol C6H6

convert moles C6H6 to kJ using delta H and the coefficients

1 mol C6H6 = +630 kJ

0.441662 mol C6H6 (630kJ / 1 mol C6H6)

=278.24706 kJ

278 kJ is absorbed, q=+278kJ