Chemical Reactions and Equations PDF

Do You Know? A solution of slaked lime produced by the reaction 1.13 is used for whitewashing walls. Calcium hydroxide reacts slowly with the carbon dioxide in air to form a thin layer of calcium carbonate on the walls. Calcium carbo...

Do You Know? A solution of slaked lime produced by the reaction 1.13 is used for whitewashing walls. Calcium hydroxide reacts slowly with the carbon dioxide in air to form a thin layer of calcium carbonate on the walls. Calcium carbonate is formed after two to three days of whitewashing and gives a shiny finish to the walls. It is interesting to note that the chemical formula for marble is also CaCO3. Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l) (1.14) (Calcium (Calcium hydroxide) carbonate) Let us discuss some more examples of combination reactions. (i) Burning of coal C(s) + O2(g) → CO2(g) (1.15) (ii) Formation of water from H2(g) and O2(g) 2H2(g) + O2(g) → 2H2O(l) (1.16) In simple language we can say that when two or more substances (elements or compounds) combine to form a single product, the reactions are called combination reactions. In Activity 1.4, we also observed that a large amount of heat is evolved. This makes the reaction mixture warm. Reactions in which heat is released along with the formation of products are called exothermic chemical reactions. Other examples of exothermic reactions are – (i) Burning of natural gas CH4(g) + 2O2 (g) → CO2 (g) + 2H2O (g) (1.17) (ii) Do you know that respiration is an exothermic process? We all know that we need energy to stay alive. We get this energy from the food we eat. During digestion, food is broken down into simpler substances. For example, rice, potatoes and bread contain carbohydrates. These carbohydrates are broken down to form glucose. This glucose combines with oxygen in the cells of our body and provides energy. The special name of this reaction is respiration, the process of which you will study in Chapter 6. C6H12O6(aq) + 6O2(aq) → 6CO2(aq) + 6H2O(l) + energy (1.18) (Glucose) (iii) The decomposition of vegetable matter into compost is also an example of an exothermic reaction. Identify the type of the reaction taking place in Activity 1.1, where heat is given out along with the formation of a single product. Chemical Reactions and Equations 7 2024-25