Chemical Reactions PDF

You must have observed that magnesium ribbon burns with a dazzling white flame and changes into a white powder. This powder is magnesium oxide. It is formed due to the reaction between magnesium and oxygen present in...

You must have observed that magnesium ribbon burns with a dazzling white flame and changes into a white powder. This powder is magnesium oxide. It is formed due to the reaction between magnesium and oxygen present in the air. Activity 1.2 Activity 1.3 n Take lead nitrate n Take a few zinc granules in a conical flask or a test tube. solution in a test n Add dilute hydrochloric acid or sulphuric acid to this tube. (Fig. 1.2). n Add potassium CAUTION: Handle the acid with care. iodide solution n Do you observe anything happening around the zinc to this. granules? n What do you n Touch the conical flask or test tube. Is there any change in observe? its temperature? From the above three activities, we can say that any of the following observations helps us to determine whether a chemical reaction has taken place – n change in state n change in colour n evolution of a gas n change in temperature. As we observe the changes around us, we can see that there is a large variety of chemical reactions taking place around us. We will study about the various types of chemical reactions and their symbolic representation in this Chapter. Figure 1.2 1.1 CHEMIC AL EQUA CHEMICAL TIONS EQUATIONS Formation of hydrogen Activity 1.1 can be described as – when a magnesium ribbon is burnt in gas by the action of dilute sulphuric acid on oxygen, it gets converted to magnesium oxide. This description of a zinc chemical reaction in a sentence form is quite long. It can be written in a shorter form. The simplest way to do this is to write it in the form of a word-equation. The word-equation for the above reaction would be – Magnesium + Oxygen → Magnesium oxide (1.1) (Reactants) (Product) The substances that undergo chemical change in the reaction (1.1), magnesium and oxygen, are the reactants. The new substance is magnesium oxide, formed during the reaction, as a product. A word-equation shows change of reactants to products through an arrow placed between them. The reactants are written on the left-hand side (LHS) with a plus sign (+) between them. Similarly, products are written on the right-hand side (RHS) with a plus sign (+) between them. The arrowhead points towards the products, and shows the direction of the reaction. 2 Science 2024-25