Cooling Drinks: Specific Latent Heat

Topics: Specific heat capacity, Energy, Thermodynamics Pages: 20 (3751 words) Published: January 8, 2014
Cooling Drinks
1. A value for the specific latent heat of fusion for water Specific latent heat is the amount of heat energy that is needed to change the state of one kilogram of a specific substance, whether it’s boiling or melting, without increasing or decreasing the temperature of the substance. Specific latent heat of fusion is the amount of heat energy that is needed to change a specific substance from solid to liquid. The specific latent heat of fusion for water is 334 KJ/ KG. Each substance has its own specific latent heat of fusion. There is also specific latent heat of vaporisation. But this is the amount of energy needed to turn a liquid into a gas, without increasing or decreasing the temperature. Below is a graph which is showing specific latent heat of fusion takes place. As the blue line ascends the temperature increases and as the line goes towards the right the time and energy given increases. As you can see when the ice is melting the temperature is staying constant but it is still giving energy. The energy given during this period is 334 kJ. [1]

[2]

Latent heat can be calculated using the following formula:

Where QL is the quantity of the heat in joules,
M is the mass in kg and l is the latent heat of the substance in J/kg

2. A value for the specific heat capacity of water

The specific heat capacity of a substance is the amount of heat energy that is needed to change the temperature of 1 kg of the substance by 1°C. Different substances have different specific heat capacities. The specific heat capacity of water is 4181 KJ. Water has quite a high specific heat capacity because water is useful for storing heat energy, and for transporting the heat energy for example in the central heating system heat is transferred via water. The standard way of finding out how much energy is needed to change the temperature of a substance is E= M*C*θ.

E is the energy transferred in joules, J
M is the mass of the substances in kg
C is the specific heat capacity in J / kg °C
Θ (‘theta’) is the temperature change in degrees Celsius, °C [3]

Each substance has a different specific heat capacity. The formula above will help you find out how much energy is needed for a certain substance to change it temperature by 1oc The specific heat capacity is the amount of heat required to change a unit mass of a substance by one degree in temperature, the difference between heat and temperature is that temperature measures how hot a substance is therefore the unit is oc. However, heat is a measure of how much kinetic energy a substance has.

3. Why energy is needed to melt ice and how this is explained by the structures of ice and water?

When a material is heated, you are adding kinetic energy to its molecules and usually raising its temperature. But when the material reaches its melting or boiling points the temperature does not increase it or decrease it stay constant while melting or boiling. At those two temperatures, the heat energy goes into changing the state of the material. After the state has changed, the temperature will rise again with added heat. But during the boiling or melting processes the heat is still being given. The energy is used to break the intermolecular bonds between the molecules.

While melting, the heat energy is needed to because the particles in a solid, in this case ice, are more packed together and in a liquid, in this case water; the particles are freer flowing. The heat energy is needed as it provides kinetic energy which would make the particles in the substance move more as the intermolecular bonds have been broken and the kinetic energy makes the particles freer flowing. [4]

[5]

4. Why is ice more effective for cooling drinks than cold water?

Ice is colder than room temperature water. Due to the fact that ice molecules move slowly and group tightly together, they produce a quite a low amount of heat. When ice...
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