Module 2:Unit 12. Specific Heat
Specific Heat
A special physical property of a substance is Specific heat. (SH). It is defined as the ability of a substance to absorb heat. Specific heat can be determined using the mass(m), thermal energyH and temperature difference(∆T).
Since specific heat is the measure of absorb or releasing heat by a substance, higher the specific heat values, smaller the temperature change for a substance.
Specific Heat(SH)=
Heat (H)
= cal or Joule/g0C
Mass(m) *∆T( T2-T1)
Metals have low specific heat, water has high specific heat. the larger the specific heat of a substance, the less temperature will change when it absorbs a particular amount of energy.
Specific heat of water is 1 cal/g0C or 4.184 J/ g0C. It is considered to be very high compared to all other liquids and solids. That means water can absorb or release a lot of heat energy without much change in temperature. Water absorbs a large amount of heat with only a small change in temperature. Water has very high specific heat because of its very strong intermolecular force. On the other hand, since amount of heat energy released is equal to amount of heat energy gained , water releases lot of energy with a negligible change in temperature. That is why climate of inner-land and coastal areas are different. All other specific heat values of substances are given at the end of the section:
Each material has different heat capacity and heats up differently. The following figure can help you to understand. For example, gold has lower heat capacity than Al. Therefore gold absorbs heat quicker than Aluminum.
In the above picture, Can you predict which substance will require more heat and why?
Watch the following video to determine the heat using specific heat capacity.
Example: Calculate the heat required in Joule to change the temperature of 25.0 g of water from 25.00C to 75.00C?
Heat= m* SH * ∆T
= 25.0 g × 4.18 J × ( 75.0-25.0) 0C
g0C
=5.23 × 103 J = 5.23 kJ
Standard Specific Heat of common substance at 20 C
| Substance | c in J/gm K | c in cal/gm K or Btu/lb F |
Molar C J/mol K |
| Aluminum | 0.900 | 0.215 | 24.3 |
| Bismuth | 0.123 | 0.0294 | 25.7 |
| Copper | 0.386 | 0.0923 | 24.5 |
| Brass | 0.380 | 0.092 | … |
| Gold | 0.126 | 0.0301 | 25.6 |
| Lead | 0.128 | 0.0305 | 26.4 |
| Silver | 0.233 | 0.0558 | 24.9 |
| Tungsten | 0.134 | 0.0321 | 24.8 |
| Zinc | 0.387 | 0.0925 | 25.2 |
| Mercury | 0.140 | 0.033 | 28.3 |
| Alcohol(ethyl) | 2.4 | 0.58 | 111 |
| Water | 4.186 | 1.00 | 75.2 |
| Ice (-10 C) | 2.05 | 0.49 | 36.9 |
| Granite | .790 | 0.19 | … |
| Glass | .84 | 0.20 | … |
Ref: http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/sphtt.html
Watch the following video:
Questions:
1. How much energy is required to heat 28.0 g of Lead from 200C to 1500C? Report your answer in Joule. Specific heat of Lead 0.128 J/g0C.
2. Consider two beakers containing compounds “X” and “Y” respectively with same mass at the same initial temperature. The final temperature of compound X is 750C and compound Y is . 630C. Which compound has higher specific heat? X or Y?
3. On the heating curve below, draw the composition of substance at each level.
4. It takes 37 .0 cal of heat to raise the temperature of 12.0 g of a substance by 8.5 0C. What is the specific heat?
5. How much energy is lost or absorbed in each of the following? Write your answer both in Joule and calorie.
a. The energy needed to heat 50.0 g of water from 15.0 0C to 50. 0C
b. The energy lost when 250 g of aluminum is cooled from 125 0C to 50. 0C
3. How many Calories are contained in a sample of olive oil that has 20.0 g of fat?
Ans: 1. 466 J
2.see your instructor
3. 180. Cal.
4. 0.363 cal/g0C
5. 1700 J