2.0kg of water at 0 degree celsius is to be changed into ice at this temperature. The same mass of water now at 100 degree celsius is to be changed into steam at this temperature.
specific latent heat of fusion of water= 3.34 x10^5 J kg^-1.
specific latent heat of vaporization of water=2.26x10^6 J kg^-1
a)calculate the amount of energy needed to be removed from the water to freeze it.
b)calculate the amount of energy required by the water to vaporize it.
c)explain the difference between the values calculated in a) and b).
help
a) To freeze the water, we need to remove the heat energy from it until it reaches the freezing point. The amount of energy needed to freeze the water can be calculated using the equation:
Energy = Mass x Specific latent heat of fusion
Given:
Mass of water = 2.0 kg
Specific latent heat of fusion = 3.34 x 10^5 J kg^-1
So, the energy required to freeze the water is:
Energy = 2.0 kg x (3.34 x 10^5 J kg^-1)
= 6.68 x 10^5 J
Therefore, the amount of energy needed to be removed from the water to freeze it is 6.68 x 10^5 J.
b) To vaporize the water, we need to supply heat energy to it until it reaches the boiling point. The amount of energy required to vaporize the water can be calculated using the equation:
Energy = Mass x Specific latent heat of vaporization
Given:
Mass of water = 2.0 kg
Specific latent heat of vaporization = 2.26 x 10^6 J kg^-1
So, the energy required to vaporize the water is:
Energy = 2.0 kg x (2.26 x 10^6 J kg^-1)
= 4.52 x 10^6 J
Therefore, the amount of energy required by the water to vaporize it is 4.52 x 10^6 J.
c) The difference between the values calculated in a) and b) is due to the different physical processes involved. In freezing, we need to remove heat energy from the water to lower its temperature until it reaches the freezing point. On the other hand, in vaporization, we need to supply heat energy to the water to increase its temperature until it reaches the boiling point. The specific latent heat of fusion and specific latent heat of vaporization represent the amount of energy required per unit mass to undergo these phase changes. The higher value for the specific latent heat of vaporization indicates that more energy is needed to change water from liquid to gas compared to changing it from a solid to a liquid.
To calculate the amount of energy needed to freeze the water, we can use the formula:
Q = mL
where Q represents the energy, m represents the mass, and L represents the specific latent heat of fusion.
a) The mass of water is given as 2.0 kg. Since we want to freeze it, the change in temperature is from 0 degrees Celsius to 0 degrees Celsius, which means there is no change in temperature. Therefore, the energy required to freeze the water is:
Q = 2.0 kg * 3.34 x 10^5 J kg^-1
b) To calculate the amount of energy required to vaporize the water, we can again use the formula:
Q = mL
Here, the mass and specific latent heat are the same as before since it is the same mass of water. However, this time the change in temperature to vaporize the water is from 100 degrees Celsius to 100 degrees Celsius.
Q = 2.0 kg * 2.26 x 10^6 J kg^-1
c) The difference between the values calculated in a) and b) is due to the difference in specific latent heat. The specific latent heat of fusion (3.34 x 10^5 J kg^-1) is the amount of energy needed to change a substance from solid to liquid or vice versa at the same temperature. On the other hand, the specific latent heat of vaporization (2.26 x 10^6 J kg^-1) is the amount of energy needed to change a substance from liquid to gas or vice versa at the same temperature.
So, the specific latent heat of vaporization is much higher than the specific latent heat of fusion because it requires more energy to change a substance from a liquid state to a gas state compared to changing it from a solid state to a liquid state.
For exam preparation
a and b are strightforward calculations.
c. The difference is due to the energy needed to remove water molecules from their common attraction when liquid: In vaporizaiton, they are removed completely. In freezing, they are not removed at all. And, in freezing, you remove energy from them, in vaporization, you add energy to them.