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The key points covered in this video include:
1. Specific Heat Capacity
2. Latent Heat of Vaporisation
Specific Heat Capacity of Water
The temperature of a substance is a measure of the average kinetic energy of the particles. When a substance is heated, the heat energy is transferred to kinetic energy, resulting in a rise in temperature. When water is a liquid, as the water molecules move past each other, hydrogen bonds are continuously made and broken. As water is heated, some of the heat energy must be used to break the hydrogen bonds in order for the water molecules to move. Therefore, more heat energy is needed to increase the kinetic energy and therefore the temperature of water than for other liquids. This means that water has a high specific heat capacity. Specific heat capacity is the amount of heat energy required to raise the temperature of 1g of a substance by 1oC. For water, the specific heat capacity is 4.2J. This high specific heat capacity means that water does not heat up or cool down very easily. This is a property of water that is essential for life because: Lakes and seas stay at a stable temperature for organisms living in them, The water inside cells can provide a stable environment necessary for enzymes to function effectively.
Latent Heat of Vaporisation of Water
In order for water to change state from a liquid to a gas, the hydrogen bonds between the water molecules must be broken. As hydrogen bonds are stronger than most intermolecular forces, a relatively high amount of energy must be used to break the bonds. This means that water has a high latent heat of vaporisation. Latent heat of vaporisation is the amount of energy needed to
vaporise 1g of substance. When water evaporates, the water molecules that are able to break their hydrogen bonds have the highest kinetic energy. When these molecules escape to become gas, this results in a decrease of the average kinetic energy of the remaining water molecules. This therefore lowers the temperature of the water - evaporation has a cooling effect. Humans use the evaporation of sweat as an effective way of reducing body temperature. Plants can also be cooled as water evaporates from mesophyll cells in the leaves and diffuses into the air.
Summary
The hydrogen bonding in water gives water many unique thermal properties that are essential for life
In order for a liquid to become a gas, the intermolecular forces between the particles must be broken
The hydrogen bonds between water molecules require more energy to break than most intermolecular forces
Water therefore has a high boiling point and remains liquid at room temperature
This allows water to provide a habitat for aquatic animals and act as a transport and reaction medium
When water is a liquid, the hydrogen bonds must be broken for water molecule to move
More heat energy is needed to increase the kinetic energy of water molecules and therefore the temperature
Water therefore has a high specific heat capacity so it provides a stable environment
The energy needed to break the hydrogen bonds at the point of vaporisation is high - water has a high latent heat of evaporation
As water molecules evaporate, this lowers the average kinetic energy of the remaining water, decreasing the temperature
This can be used to help cool organisms down
23 мар 2019
