Question

Calculate the energy in joules required to heat 7.25 of water from 1.5 to 68.8.

Answer 1

units? 7.25 what, 1.5 to 68.8 what

Answer 2

basically the equation will be\[\Delta H=Cp*\Delta T\] where Cp is the specific heat. and this is just for 1 mole of water so the 7.25 whatever will be devided by water molecular weight (18 grams/mole).
Delta H in this system is equal as the heat, where heat is the energy.
now you do the math, look for Cp of water in google with the units you need

Answer 3

oh sorry heat 7.25grams and then 1.5 degrees Celsius to 68.8 degrees Celsius

Answer 4

Cp of water is 4.2KJ/KgKelvin, 7.25 g of H2O=.402 mol. wont help you any further than this

Answer 5

The equation you're looking for is q = mcΔT.

q = total energy required to produce temperature change (what you're looking for)
m = mass
c = specific heat (J/g/C)
ΔT = temperature change

Plug n' play :P

Answer 6

@matt101
m its not mass, its moles. not the same

Answer 7

Actually, in this equation it is. Specific heat capacity is the amount of energy needed to raise one GRAM of a substance by one degree C (or K). Molar heat capacity is what you're talking about, the amount of energy needed to raise one MOLE of a substance by one degree C (or K). In that case, the equation would be q = ncΔT, where n is the moles and c is the molar heat capacity.

You can solve the question @nasoff gave by finding moles from the mass given, but its an extra step in this case since you can solve directly using the mass. Also, the equation you provided would not help as it uses enthalpy, with units of J/mol, and so there would be no way of figuring out the absolute amount of heat required in this specific situation.