Question

11. Calculate enthalpy of rx using the following information (enthalpy of formation, or enthalpy of rx of other chemical reactions

12. How much energy is released when 2.0 g of methane is combusted in open air (given the enthalpy of reaction).

13. If 1.00 g of ethanol is burned and heats up 100g of water by 5 degrees, what is the heat of combustion of ethanol? (given the specific heat capacity of water)

Answer 1

for methane

CH4 + O2 =CO2 + H2O

balance

CH4 + 2O2 =CO2 + 2H2O

HRXN = Hproducts -Hreactants = -393.5 + 2*-241.8 - (-74.6 + 2*0) = -802.5 kJ/mol

then..

2 g of methane --> mol = masS/MW = 2/16= 0.125

1 mol = 802.5 kJ released

0.125 mol --> 0.125*802.5 = 100.3125 kJ will be released

the... for ethanol

C2H5OH + O2 = CO2 + H2O

balance

C2H5OH + 7/2O2 = 2CO2 + 3H2O

mol of ethanol = mass/MW = 1/46= 0.021739

Q = m*C*(Tf-Ti) = 100*4.184*5 = 2092 J

Hrxn = -2092/0.021739

Hrxn = -96232.57 J/mol = -96.23 kJ/mol