Answer the following:
a) Liquefied petroleum gas is used in kitchens. When the gas is in a cylinder, it is in the liquid state. When it comes out of the cylinder it becomes a gas (change A), then it burns (change B). Identify the processes A and B.
b) How does the ozone layer in the atmosphere protect us from harmful ultraviolet rays?
[5 MARKS]
Answer the following:
a) Liquefied petroleum gas is used in kitchens. When the gas is in a cylinder, it is in the liquid state. When it comes out of the cylinder it becomes a gas (change A), then it burns (change B). Identify the processes A and B.
b) How does the ozone layer in the atmosphere protect us from harmful ultraviolet rays?
[5 MARKS]
Option a) Identification and Explanation of each change: 1.5 Marks
Option b): 2 Marks
a) LPG is in a liquid state inside the cylinder. However, when it comes out of the cylinder it becomes a gas. So, it is a physical change, because no new substance is formed. It is only a change in state.
When the gas comes out and burns, it is a chemical change, because the LPG gas burns with oxygen and forms carbon dioxide. Heat is also released while burning the gas.
So, change A is a physical change while change B is a chemical change.
b) The ozone layer protects us from harmful ultraviolet rays which come from the sun. Ozone absorbs this radiation and breaks it down into oxygen. In this process, a new substance is formed, so it is a chemical change. If the ultraviolet rays are not absorbed by the ozone layer, these harmful rays would reach the earth's surface and cause harm to us and other life forms.
Option a) Identification and Explanation of each change: 1.5 Marks
Option b): 2 Marks
a) LPG is in a liquid state inside the cylinder. However, when it comes out of the cylinder it becomes a gas. So, it is a physical change, because no new substance is formed. It is only a change in state.
When the gas comes out and burns, it is a chemical change, because the LPG gas burns with oxygen and forms carbon dioxide. Heat is also released while burning the gas.
So, change A is a physical change while change B is a chemical change.
b) The ozone layer protects us from harmful ultraviolet rays which come from the sun. Ozone absorbs this radiation and breaks it down into oxygen. In this process, a new substance is formed, so it is a chemical change. If the ultraviolet rays are not absorbed by the ozone layer, these harmful rays would reach the earth's surface and cause harm to us and other life forms.
