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The heats of combustion of C x H y , carbon and hydrogen are a, b and c cal respectively. The heat of formation of C x H y , will be:

Options

  1. A- x b + y c 2 - a 2 cal
  2. B- x b + y c 2 - a cal
  3. Cx b - y c 2 + a 2 cal
  4. Dx b - y c 2 - a 2 cal

Correct answer

B. - x b + y c 2 - a cal

Step-by-step solution

xC   +   y 2 H 2 → C x H y                     ΔH f CxHy   =   ? ΔH f CxHy   =   ΔH rx n = ΔH comb . CxHy − xΔH comb . C − y 2 ΔH comb . H 2 =   a − x b − y 2 c =   − xb   +   yc 2 − a   cal

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