Answer to Question #297134 in General Chemistry for Barbara Cavalcanti

Question

Q8.

Calculate the standard free energy change for the combustion of methane at 25^oC. Assume that all reactants and products are gases. Provide an answer correct to 3 significant figures. Do not use scientific notation or include units to report your answer.

Answer 1

$CH_{4(g)}+2O_{2(g)}\to\>CO_{2(g)}+2H_2O_{(g)}$

$C_{(s)}+2H_{2(g)}\to\>CH_{4(g)}$ $\Delta\>H_f^\theta=-74.9kJ/mol$

$C_{(s)}+O_{2(g)}\to\>CO_{2(g)}\>\>\>\Delta\>H_f^\theta=-393.5kJ/mol$

$2H_{2(g)}+O_{2(g)}\to\>2H_2O_{(g)}\>\>\Delta\>H_f^\theta=-241.8kJ/mol$

$\Delta\>H_{comb}^\theta(CH_4)=\Delta\>H_f^\theta(CO_2)+2\Delta\>H_f^\theta(H_2O)-\Delta\>H_f^\theta(CH_4)$

$=-393.5+2(-241.8)-(-74.9)$

$=-802.2kJ/mol$

$=-802$