Thermal Energy- ANSWER KEY
1. A 10.0 g piece of copper wire, sitting in the sun reaches a temperature of
80.0˚C. How many Joules are released when the copper cools to 40.0˚C? The
specific heat capacity of copper is 0.377 J/(g.˚C).
First: write down your givens
Mass (m) = 10 g
Initial temperature (Ti) = 80˚C
Final temperature (Tf) = 40 ˚C
Specific heat capacity = 0.377 J/(g.˚C)
The formula to find heat (Q) (or thermal energy) = m c Δ T
Remember that Δ T = Tf - Ti
Next: Plug your givens in your formula
Q= (10) (0.377) (80- 40)
Q= 150.8 Joules
2. The specific heat capacity of water is 4.184 J/(g.˚C). How much thermal
energy is required to change the temperature of 700.0g of water from 25.6˚C
to 75.4 ˚C?
Givens: c = 4.184 J/(g.˚C)
m = 700 g
The formula for thermal energy is
Q = (700) (4.184) (75.4-25.6)
Q= 145, 854.24 Joules
Tf= 75.4˚C
Q= m c ΔT
Ti = 25.6˚C
3. How much thermal energy is released when a 201g piece of blown glass at an
initial temperature of 150˚C is cooled to 25˚C? The specific heat capacity of
glass is 0.837 J/(g.˚C).
Givens: c = 0.837 J/(g.˚C)
m = 201 g
The formula for thermal energy is
Tf= 25˚C
Ti = 150˚C
Q= m c ΔT
Q = (201) (0.837) (25-150)
Q= - 21,029.625 Joules
4. If 2077 J are released to change the temperature of a block of ice initially at a
temperature of -20˚C to 0˚C, find the mass of the ice. Ice has a specific heat
capacity of 2.077 J/(g.˚C).
Givens: c = 2.077 J/(g.˚C)
m=?g
Tf= 0˚C
Ti = - 20˚C
Q= -2077 J (Q is negative because energy is RELEASED)
The formula for thermal energy is
Q= m c ΔT
-2077 = (m) (2.077) (0- (-20))
- 2077 = m (41.54)
m= -2077/ 41.54
m= - 50
Since we are finding mass, answer should be a positive answer.
m= 50 grams
5. Mercury has a specific heat capacity of 0.139 J/(g.˚C). How many Joules are
required to change the temperature of a 50.0 g sample of Mercury from
20.7˚C to 100.4˚C.
Givens: c = 0.139 J/(g.˚C)
The formula for thermal energy is
Q = (50) (0.139) (100.4 – 20.7)
Q= 553.915 Joules
m = 50 g
Q= m c ΔT
Tf= 100.4˚C
Ti = 20.7˚C
6. A balloon is filled with 0.5 g of air, which has a specific heat capacity of 1.046
J/(g.˚C). How many Joules are required to change the temperature from 20˚C
to 30˚C?
Givens: c = 1.046 J/(g.˚C)
m = 0.5 g
The formula for thermal energy is
Tf= 30˚C
Ti = 20˚C
Q= m c ΔT
Q = (0.5) (1.046) (30-20)
Q= 9.96 Joules
7. A 25g block of sugar requires 781 Joules to change the temperature from
25˚C to 50˚C. What is the specific heat capacity of sugar?
Givens: c = ? J/(g.˚C)
m = 25 g
The formula for thermal energy is
Tf= 50˚C
Ti = 25˚C
Q= 781 Joules
Q= m c ΔT
781 = (25) (C) (50-25)
781= c (625)
C= 781/625
C= 1.2496 J/(g.˚C)
8. When a 400.0 g f ammonia is cooled from a temperature of 25˚C to 10˚C,
13,054 Joules of thermal energy are released. Find the specific heat capacity
of ammonia.
Givens: c = ? J/(g.˚C)
m = 400 g
The formula for thermal energy is
Tf= 10˚C
Ti = 25˚C
Q= 13,054 Joules
Q= m c ΔT
13,054 = (400) (c) (10-25)
13,054 = c (400)(-15)
13,054 = c (6000)
------->
c = 13,054/6000 = 2.176 J/(g.˚C)