Wednesday
May 4, 2016

# Homework Help: chemistry

Posted by maria on Saturday, October 26, 2013 at 7:41pm.

A typical bathtub can hold 106 gallons of
water. Calculate the mass of natural gas that
would need to be burned to heat the water
for a tub of this size from 56 ◦F to 87 ◦F.
Assume that the natural gas is pure methane
(CH4) and that the products of combustion
are carbon dioxide and water (liquid).

2nd part
What volume of natural gas does this correspond to at 30◦C and 1 atm?
• chemistry - DrBob222, Saturday, October 26, 2013 at 8:30pm

a.
1. Convert F to C. Convert 106 gallons H2O to L, assume density of 1.0 g/mL and convert L to grams.
2. Calculate q = heat required to heat the water as described.
q = mass H2O x specific heat H2O x (Tfinal - Tinitial).

3. Write and balance the equation for the combustion of CH4.
CH4 + 2O2 ==> CO2 + 2H2O

4. Calculate heat of combustion.
dHfrxn from step 2 = (n*dHf products) - (n*dHf reactants). Call this dHrxn

5. dHrxn in kJ/16g CH4 x # g CH4 = q
Solve for #g CH4

Check my thinking.

b.
Use PV = nRT and solve for V in L. You will need to plug in for n; remember n = grams/molar mass. You know g and molar mass so you can calculate n and obtain V from there.