Answer
Q=4479.8 cal
Procedure
To solve the problem you will need to use the specific heat formula
[tex]Q=mc\Delta T[/tex]Where;
Q=heat energy
m=mass
c=specific heat capacity
ΔT=change in temperature
Assuming that the heat released from the cracker of unknown material is equal to the heat absorbed by the water, then we can use the c and m for water in our calculations.
[tex]c_{water}=4.186\frac{J}{g\degree C}[/tex]Substituting the values in our equation we have
[tex]Q=mc\Delta T=81.6\text{ }g(4.186\frac{J}{g\degree C})(68.1-13.2)\degree C=18752.61\text{ }J[/tex]Finally, transform the J to cal
[tex]18752.61\text{ }J\frac{1\text{ }cal}{4.186\text{ }J}=4479.8\text{ cal}[/tex]