I burned a candle for 3 minutes. It started with a mass of 38.53g (C25H52). It ended with a mass of 38.48g. What mass of water was produced in three minutes? If I burned the candle all day, what mass of the candle would react?

Answer 1

2C25H58 + 79O2 ==> 50CO2 + 58H2O

mols C25H58 = (38.53-38.48)/molar mass = about 0.00014 but you should be more accurate.
Convert mols C25H58 to mol H2O using the coefficients in the balanced equation.
Now convert that to grams. g = mols H2O x molar mass H2O.