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Heat Capacity of Water

What is Heat Capacity?

• Heat capacity is the amount of heat required to raise the temperature of an object by one unit.

• The specific heat capacity is the heat required to raise one gram of a substance by one temperature unit.

• Example: The specific heat capacity of Iron is $0.450\frac{J}{g°C}$. So it takes 0.450 joules of energy to raise the temperature of 1 gram of iron by 1°C.

• To calculate the specific heat capacity, use the formula: $C = \frac{Q}{mΔT}$.

• $C$ is the specific heat capacity.
• $Q$ is the total heat energy.
• $m$ is the mass.
• ΔT is the change in temperature.

• A negative temperature change means the process is exothermic. A positive temperature change means its endothermic.

• When do we use specific heat capacity?

• The specific heat capacity calculation is most commonly used in calorimetry experiments. A calorimeter is an instrument that measures the enthalpy change of a combustion reaction.

• We also use it for phase changes. See our lessons on heating and cooling curves and the phase change diagram of water for more information.

• What does a high/low heat capacity mean?

• A high heat capacity means that the substance requires lots of heat in order to raise or lower the temperature by one unit. Having a high heat capacity means that the substance also retains heat better than substances with lower heat capacities.

• A low heat capacity means that the substance does not require a lot of heat in order to raise/lower the temperature by 1°C. A low heat capacity means that the substance does not retain heat as well as substances with a higher heat capacity.

Heat Capacity of Water

• The specific heat capacity of water is $4.182 \frac{J}{g°C}$, $4184.0\frac{J}{kg°C}$, or 1 calorie (cal).

• Water has a very high heat capacity compared to other substances. So, it takes more energy to raise the temperature of water by 1 degree than other substances. This also means that water will retain heat better than other substances.

• If you left 100°C water and 100°C Iron out for 5 minutes, the iron would have lost more heat than water would. So, the iron would be cooler than the water because water retains heat better.

• Why does water have such a high heat capacity?

• Water is a polar covalent molecule.

• There is a huge electronegativity difference between the oxygen and hydrogen atoms. So, the oxygen atom pulls the electron density towards it.

• The polarity in conjunction with its bent molecular geometry creates a permanent dipole.

• Water's hydrogen bonding means there are more electrostatic interactions between its molecules compared to other liquids. So, water can absorb more energy before vaporizing. That's why it's often used as a coolant. For example, when we study nuclear chemistry, we'll see that it's used as a coolant in nuclear power plants.

• Why is this important?

• The heat capacity of water is actually very important. The heat capacity of water plays a role in our climate, and it's the reason why many places are habitable.

• Because it takes a lot of energy to gain/lose temperature, it makes water habitable because it does not constantly fluctuate in temperatures. This allows marine life to live in the ocean!

• Also humans are composed of about 70% water, and this is also a reason why our own body temperatures do not fluctuate that much!

(Video) Heat Capacity

by ADLC Educational Media

Why do people run from the hot sand into the cool ocean on a sunny summer day? The cool, refreshing water temperature comes from water's high specific heat capacity. This refers to the amount of heat it can absorb before its temperature changes.

This quick video explains what is meant by specific heat or heat capacity. It shows how common substances (sand and water) absorb heat at different rates. Finally, we get to see this in action with a cool experiment at the end.

(Video) Specific Heat of Water

by Forsyth Tech CTL

This animation shows what happens when water is boiled on a molecular level. It's a great way to visualize hydrogen bonds breaking. Keeping this animation in mind, you will be able to easily understand why water can absorb so much heat before its temperature rises.