E. Long answer questions.
1. Differentiate between the following and give examples.
a. Physical and Chemical changes
b. Reversible and Irreversible changes
2. Name the three states in which water exists. How can we change them into one another?
3. Explain the factors on which the solubility of a substance in water depends?
Answers
Explanation:
Difference Between Physical and Chemical Change
Such changes which do not produces any new substances after the reaction is called as the physical change, whereas the changes which bring out the formation of new substance is named as the chemical change. So we can say that the main difference lies in the chemical composition, where one (chemical change) of the change is involved in altering the composition of the material and thus forms new substance and the other (physical change) brings out alteration in size, shape and colour only.
b
All changes in the world are one of the two types – Reversible changes and irreversible changes. A change which can happen backward, that is, can be reversed is called a reversible change. If you keep water in the freezer for some time, it transforms into ice. But as soon as you take it out of the freezer, it turns into water again. This is a reversible change. Similarly, if you boil water, it evaporates and becomes water vapor. When you cool this vapor down, it turns back to water. A change which cannot happen backward, that is, it cannot be reversed is called an irreversible change. When you burn a piece of paper, it turns to ash. It cannot become paper again. Your height cannot decrease. These are irreversible changes. They cannot be reversed at all.
c
Just like any substance, water can exist in three different forms, called states: solid, liquid and gas. The state will change when the substance is heated,freezed or melted
d
Solubility is the ability of a solid, liquid, or gaseous chemical substance (referred to as the solute) to dissolve in solvent (usually a liquid) and form a solution. The solubility of a substance fundamentally depends on the solvent used, as well as temperature and pressure. The solubility of a substance in a particular solvent is measured by the concentration of the saturated solution. A solution is considered saturated when adding additional solute no longer increases the concentration of the solution.
Answer:
1) A)The difference between a physical reaction and a chemical reaction is composition. In a chemical reaction, there is a change in the composition of the substances in question; in a physical change there is a difference in the appearance, smell, or simple display of a sample of matter without a change in composition.
B) Reversible changes - where a change is made physically and can be undone or reversed. For example: freezing water to make ice.
Irreversible changes - where the change is made chemically and can't be reversed into its original states. For example: baking a cake.
2)Just like any substance, water can exist in three different forms, called states: solid, liquid and gas. The state will change when the substance is heated.
3)Solubility is the maximum amount of a substance that will dissolve in a given amount of solvent at a specific temperature. There are two direct factors that affect solubility: Temperature and pressure affects the solubility of both solids and gases, but pressure only affects the solubility of gases.
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