3. Combustion is a hydrocarbon compound a reaction where (that contains hydrogen

Question

3. Combustion is a hydrocarbon compound a reaction where (that contains hydrogen and carbon) reacts with gaseous oxygen to produce gaseous carbon dioxide and liquid water. much How gas phase ethane (CHSmust be burned in a combustion reaction to form 100 kJ of heat? Would the sign for the change in heat be positive or negative? Why? (15 points) CH3OH (1) CHCOOH (g) C2H4 (g) C2H2 (g) CO (g) CH4 (g) CH6 (g) On (g) CO2 (g) AHF = -239 KJ AHS = -432 KJ AH =-75 KJ AHr =-239 KJ AH = OJ AHF = -394 KJ AHf = +52 kJ AH = +226 KJ AHF = -111 kJ AHr = -286 KJ AH = -188 KJ H2O (W) H2O2 (1)

Explanation / Answer

i)2C2H6(g) + 7O2(g) --------> 4CO2(g) + 6H2O(l)

Hr = Hf(products) - Hf(reactants)

=( 4×Hf(CO2) + 6×Hf(H2O) ) - ( 2×Hf(C2H6) )

= ( 4×(-394kJ) + 6×(-286kJ) ) - ( 2×-239kJ)

= -3292kJ - 478kJ

=- 3770kJ

Therefore, 1mole of C2H6 give 1885kJ

Mole of C2H6 required for 100kJ = (1mol/1885kJ)×100kJ = 0.05305mol

Molar mass of C2H6 = 30.07g/mol

Mass of C2H6 rquired = 0.05305mol × 30.07g/mol = 1.5952g

ii) The sign of heat change is negative because heat is released from this reaction

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