Question

When 9.00 g of methane, CH4(g), is burned in a constant pressure calorimeter with a heat capacity of 66.0 kJ·K–1 , the temperature of the calorimeter assembly rises by 7.59 K. What is the standard enthalpy of combustion of methane? A. –281 kJ·mol–1 B. –1252 kJ·mol–1 C. –891 kJ·mol–1 D. –31.3 kJ·mol–1 E. –501 kJ·mol–1

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Answer 1

For combustion of reaction the reaction involved is

CH4 + O2 ---------> CO2 + H2O

The standard enthaply of combustion is essentially energy released when 1 mole of the compound is rescted in presence of oxyen

The amount of heat released by 9 g of methane is = nCpt ( For 9 g of methane mun=ber of moles = 9 /16 = 0.5625

= 0.5625 * 66 KJK-1* 7.59 K

= 281.77 KJ mol

For 0.5625 moles amount of energy released = 281.77 KJ

for 1 mole amount of energy released =(281.77 /0.5625)* 1 = 500.92 KJ / mol

AS THE HEAT IS RELEASED SO THE NEGAIVE SIGN IS INCLUDED

So the Enthalpy of combustion of methne is = -501 KJ / mol