Name_________KEY___________________
Chemistry
Date______________________
Unit: The Chemistry of Biofuels
Heat Calculations Assignment
Specific Heat
1. Rearrange the equation, algebraically, for specific heat, cp = q/m·∆T , to solve for :
a) Final temperature Tf = __q___ + Ti
cp m
b) Mass m = __q___
cp ∆T
a) Heat energy q= cp m∆T
2. How much heat is needed to raise the temperature of a 55g sample of aluminum from
22.4˚C to 94.6˚C? The specific heat (cp) for aluminum is 0.897 J/g·˚C.
3.56 kJ
3. A total of 3.5 kJ of heat are added to a 28.2g sample of iron at 20˚C. What is the final
temperature of the iron? The specific heat of iron is 0.449J/g·˚C.
296.72 ˚C
4. A 123.5 g sample of an unknown metal loses 235.8 J of energy as its temperature falls
from 100.8˚C to 83.5˚C. What is the specific heat of this metal?
0.11 J/g·C
*because it’s losing heat, q is negative but ∆T is also negative, giving us a positive specific heat
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Name_________KEY___________________
Chemistry
Date______________________
Unit: The Chemistry of Biofuels
Calorimetry
For these problems, assume mL = g. THIS ONLY WORKS FOR WATER because of it’s
density. The specific heat of water is 4.18 J/g·˚C.
5. A small pebble is heated and placed in a coffee cup calorimeter containing 25.0mL of
water at 25.0˚C. The water reaches a maximum temperature of 26.4˚C. How many
joules of heat were released by the pebble?
146.3 J
6. If 596 J of heat are added to 29.6g of water at 22.9˚C in a coffee cup calorimeter, what
will be the final temperature of the water?
27.72 ˚C
7. How much heat is released from a reaction occurring in a coffee cup calorimeter filled
with 135g of water, when a temperature change is observed to rise from 23.4˚C to
35.4˚C?
~ 6.77 kJ
8. How much heat is absorbed from a reaction occurring in a coffee cup calorimeter filled
with 88.4˚Cg of water, when a temperature change is observed to fall from 24.8˚C to
18.7˚C?
~ -2.25 kJ
9. Which reactions (problems) were endothermic? Exothermic? How do you know?
Endothermic 2,3, and 8 , heat is absorbed, or needed, by the system
Exothermic 4, 5, 6, and 7, heat is released, or lost, by the system
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