Chemistry_Grade_10-12 (1).pdf

Melting point is the temperature at which a solid

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Melting point is the temperature at which a solid changes its phase to become a liquid . The reverse process (change in phase from liquid to solid) is called freezing . The stronger the chemical bonds and intermolecular forces in a substance, the higher the melting point will be. Boiling point is the temperature at which a liquid changes phase to become a gas. The stronger the chemical bonds and intermolecular forces in a substance, the higher the boiling point will be. Density is a measure of the mass of a substance per unit volume. Viscosity is a measure of how resistant a liquid is to changing its form. Exercise: Summary exercise 1. Give one word or term for each of the following descriptions. (a) The property that determines how easily a liquid flows. (b) The change in phase from liquid to gas. (c) A composition of two or more atoms that act as a unit. (d) Chemical formula that gives the relative number of atoms of each element that are in a molecule. 2. For each of the following questions, choose the one correct answer from the list provided. A Ammonia, an ingredient in household cleaners, can be broken down to form one part nitrogen (N) and three parts hydrogen (H). This means that ammonia... i. is a colourless gas ii. is not a compound iii. cannot be an element iv. has the formula N 3 H B If one substance A has a melting point that is lower than the melting point of substance B, this suggests that... i. A will be a liquid at room temperature. ii. The chemical bonds in substance A are weaker than those in substance B. iii. The chemical bonds in substance A are stronger than those in sub- stance B. iv. B will be a gas at room temperature. 3. Boiling point is an important concept to understand. a Define ’boiling point’. b What change in phase takes place when a liquid reaches its boiling point? c What is the boiling point of water? d Use the kinetic theory of matter and your knowledge of intermolecular forces, to explain why water changes phase at this temperature. 4. Refer to the table below which gives the melting and boiling points of a number of elements, and then answer the questions that follow. ( Data from ) Element Melting point Boiling point ( 0 C) copper 1083 2567 magnesium 650 1107 oxygen -218.4 -183 carbon 3500 4827 helium -272 -268.6 sulfur 112.8 444.6 32
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CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10 2.6 a What state of matter (i.e. solid, liquid or gas) will each of these elements be in at room temperature? b Which of these elements has the strongest forces between its atoms? Give a reason for your answer. c Which of these elements has the weakest forces between its atoms? Give a reason for your answer. 33
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2.6 CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10 34
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Chapter 3 The Atom - Grade 10 We have now looked at many examples of the types of matter and materials that exist around us, and we have investigated some of the ways that materials are classified. But what is it that makes up these materials? And what makes one material different from another? In order to
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