Answer to Question #105173 in General Chemistry for Vanessa Clothier

Question

Methanol and methylamine are both combustible fuels. How many grams of methylamine must be combusted to raise the temperature of 385 g of water from 25.0°C to 45.0°C? Assume that the transfer of heat from the flame to the water is 100% efficient. How many grams of carbon dioxide are produced in this combustion reaction?

Answer 1

ΔT=45-25=20°C;

m(H₂O)=385 g ;

ΔH_f(CO₂) = -393.5 kJ*mol^-1;

ΔH_f(CH₃NH₂)= -23.5 kJ*mol^-1;

ΔH_f(H₂O) = -241.8 kJ*mol^-1;

с(H₂O) = 4.2 J/g°C - the specific heat capacity of water;

4CH₃NH₂ + 9O₂ = 4CO₂ + 10H₂O +2N₂ ,

ΔH= 4*ΔH_f(CO₂) + 10*ΔH_f(H₂O) - 4*ΔH_f(CH₃NH₂) = -3898 kJ*mol^-1;

It means that 3898 kJ of heat is released when 4 moles of CO₂ are produced.

Q=m*c*ΔT;

c = specific heat capacity (sometimes represented by the letter 's', or 'Cs');

Q = heat in kJ;

m = mass in kg;

Δ T = change in temperature in °C;

Q=385*4.2*20=32340 kJ ;

n(CO₂)=Q/ΔH=32340/3898=8.3 mol;

m(CO2)= n(CO2)*M(CO2)=8.3*44=365.2 g;

Answer: 365.2 grams of carbon dioxide are produced in this combustion reaction.