Name: ___________________________________
Date: _____________
Measurement of Heat
Heat (q) is energy that is in the process of flowing from a warmer object to a cooler object.
The units for heat are the same as any other form of energy: Joules (J), kiloJoules (kJ),
calories (cal), kilocalories (kcal) and nutritional calories (Cal).
4.18 Joule = 1 cal
1 Calorie = 1 kcal = 1000 cal
Specific Heat (c): The amount of heat required to raise the temperature of one gram of a
given substance by one degree Celsius.
All substances have their own unique specific heat value.
Specific heat constants are usually given in the units of J/g ºC or cal/g ºC
The specific heat of water is 4.184 J/g ºC or 1 .0 cal/g ºC. Values for other substances can
be found in a reference table.
To calculate the amount of heat that is released or gained during a temperature change, the
following equation is used:
q = m x c x ∆T
q = heat (J or cal)
m = mass (g)
c = specific heat of the substance (J/g ºC or cal/g ºC )
∆T = change in temperature (final temperature – initial temperature)
Example: Assume that 2.50 kJ of energy is absorbed by 25 grams of water. What would be
the change of temperature of the water?
To solve:
i. Be sure all given values have units required for equation; if not, convert them! 2.50 kJ
= 2.50 x 103J = 2500 J
ii.. Then plug known values into equation
q = m x c x ∆T
2500 J = 25g x 4.18J x ∆T
g oC
iii. Solve for ∆T: ∆T = 23.9oC
Complete the following practice problems. Show all work and units!
1. A 15.75-g piece of iron absorbs 1087 joules of energy, and its temperature changes
from 25°C to 175°C. Calculate the specific heat of iron.
2. How many joules of energy are needed to raise the temperature of 10.0 g of aluminum
from 22°C to 55°C, if the specific heat of aluminum is 0.90 J/g°C?
3. a. What temperature change will a 50.0 g piece of glass undergo if it absorbs 5275 joules
of heat and its specific heat capacity is 0.50 J/g°C? b. If the initial temperature of the
glass is 20.0°C what would be the final temperature?.
4. 100.0 mL of 4.0°C water is heated until its temperature is 37°C. If the specific heat of
water is 4.184 J/g°C, calculate the amount of heat energy needed to cause this rise in
temperature. Remember the density of water is 1 g/mL. This means that 1 gram of
water = 1 mL of water.
5. What is the specific heat capacity of silver metal if 55.00 g of the metal absorbs 47.3
calories of heat and the temperature rises 15.0°C?
6. What is the specific heat of a substance that absorbs 2.5 x 103 joules of heat when
a sample of 1.0 x 104 g of the substance increases in temperature from 10.0°C to
70.0°C?
7. How many grams of water would require 2.20 x 104 kilojoules of heat to raise its
temperature from 34.0°C to 100.0°C? The specific heat of water is 4.18 J/g∙°C
8. If 200. grams of water is to be heated from 24.0°C to 100.0°C to make a cup of tea,
how much heat must be added? The specific heat of water is 4.18 J/g∙°C
9. A block of aluminum weighing 140. g is heated from 62.2°C to 98.4°C with the
absorption of 1080 joules of heat. From this data, calculate the specific heat of
aluminum.
10. A cube of gold weighing 192.4g is heated from 30.0°C to some higher temperature,
with the absorption of 54.0 cal of heat. The specific heat of gold is 0.030 J/g∙°C.
What was the final temperature of the gold?
11. a. Consider two pots of water. Each pot has the same diameter, but pot A is deeper than pot B
and so there is more water in pot A. If both of the pots are exposed to exactly the same amount of
heat for five minutes on a stove, which pot will contain the hottest water after heating?
____________
b. Considering question a, propose an explanation for the fact that even though both pots were
exposed to the same amount of heat, one got hotter.
___________________________________________________
c. Fill in the blank: The greater the mass of a substance (like water in questions 1 and 2), the
____________________ the temperature change when heat is applied.
12. a. Consider the metal hood of a car on a warm sunny day. Next to the car is a large puddle of
water. The puddle of water is so large that it has the same mass as the hood of the car. Assume that
the hood of the car and the puddle are exposed to the same amount of sunlight. Which will be hotter
after two hours—the hood of the car or the puddle? __________________________
b. Propose an explanation for the fact that even though both the hood and the puddle were exposed to
the same amount of heat energy and their masses were the same, one still got much warmer than the
other.
c. In general is it harder to change the temperature of metal (like on a car hood) or of water? In
other words, would it require more heat energy to change the temperature of metal or of water?
___________What term in the mathematical equation for heat would account for this difference?
_____________________________.
d. Would you expect the specific heat constant for a metal to be higher or lower than that for
water? Look back at the definition for specific heat and examine its units and think as to what it is
telling you.
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