Question

if a 2.0g sample of water at 5.0celcius absorbs 21.8Joules of energy, the temprature of the sample will be raised by

Answer 1

You'd use the temperature change equation. The specific heat of water is always 4.18J/(g °C).
Equation to use: q=mCΔT

21.8=(2.0)(4.18)(Tf-5)
21.8=(8.36)(Tf-5)
21.8/8.36=Tf-5
2.61=Tf-5
2.61+5=Tf
Tf=7.61 °C

Since you want to know how many °C it raises, you wouldn't pay attention to the last 2 steps, however if you need to know the final temp, you want to go to the last step.