Chemistry_Grade_10-12 (1).pdf

Exercise summary exercise 1 give a word or term for

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Exercise: Summary Exercise 1. Give a word or term for each of the following phrases: (a) The continuous circulation of water across the earth. (b) The change in phase of water from gas to liquid. (c) The movement of water across a land surface. (d) The temperature at which water changes from liquid to gas. 2. In each of the following multiple choice questions, choose the one correct answer from the list provided. (a) Many of the unique properties of water (e.g. its high specific heat and high boiling point) are due to: i. strong covalent bonds between the hydrogen and oxygen atoms in each water molecule ii. the equal distribution of charge in a water molecule iii. strong hydrogen bonds between water molecules iv. the linear arrangement of atoms in a water molecule (b) Which of the following statements is false ? i. Most of the water on earth is in the oceans. ii. The hardening of surfaces in urban areas results in increased surface runoff. iii. Water conservation is important because water cannot be recycled. iv. Irrigation is one of the largest water users in South Africa. 3. The sketch below shows a process that leads to rainfall in town X. The town has been relying only on rainfall for its water supply because it has no access to rivers or tap water. A group of people told the community that they will never run out of rainwater because it will never stop raining . 367
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18.7 CHAPTER 18. THE WATER CYCLE - GRADE 10 P1 Cloud Sea P2 Town X (a) List the processes labelled P 1 and P 2 that lead to rainfall in town X. (b) Is this group of people correct in saying that town X will never run out of rainwater? Justify your answer using the sketch. Recently, the amount of rainwater has decreased significantly. Various reasons have been given to explain the drought. Some of the community members are blaming this group who told them that it will never stop raining. (c) What scientific arguments can you use to convince the community mem- bers that this group of people should not be blamed for the drought? (d) What possible strategies can the community leaders adopt to ensure that they have a regular supply of water. 368
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Chapter 19 Global Cycles: The Nitrogen Cycle - Grade 10 19.1 Introduction The earth’s atmosphere is made up of about 78% nitrogen, making it the largest pool of this gas. Nitrogen is essential for many biological processes. It is in all amino acids, proteins and nucleic acids. As you will see in a later chapter, these compounds are needed to build tissues, transport substances around the body, and control what happens in living organisms. In plants, much of the nitrogen is used in chlorophyll molecules which are needed for photosynthesis and growth. So, if nitrogen is so essential for life, how does it go from being a gas in the atmosphere to being part of living organisms such as plants and animals? The problem with nitrogen is that it is an ’inert’ gas, which means that it is unavailable to living organisms in its gaseous form. This is because of the strong triple bond between its atoms that makes it difficult to break. Something needs to happen to the nitrogen gas to change it into a form that it can be used. And at some
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