Assuming your tea cup holds10.0 mol of water (It actually does! 10 mol water is approximate 6 fl. oz.) How much heat is required to raise the temperature of your tea water from room temperature to 100 °C? The specific heat of water is 4.184 J g-1 K-1.
If you are going to work in moles you need to know the molar heat capacity
q = n Cmol T
q = (10.0 mol)(75.318 J mol-1 K-1)(100 °C - 23 °C)
q = 57,990 J
Since the water absorbs 57.990 J of heat, the reaction must release 57,990 J of heat. So,
Since you know that DHcombustion = -890 kJ/mol (because you looked it up in a book) use factor label and stoichiometry to solve the problem.
(-890 kJ was converted to -890,00 J)