Free NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations in PDF form to download. NCERT Solutions for Class 10 Science all chapters and answers given with in the chapters are also given in PDF form to download. Download books for class 10 in PDF form.
NCERT Solutions for Class 10 Science Chapter 1
Important Questions with Answers on Chemical Reactions and Equations
- Question 1:
What is meant by a skeletal chemical equation? Using suitable chemical reaction, differentiate between a skeletal chemical equation and a balanced chemical equation.
If the number of atoms of any element in a chemical equation is not equal on both sides, then it is a skeletal equation. For example: Here, the number of chlorine and hydrogen atoms are not equal on both sides.
In a Balance equation, the numbers of atoms of different elements on both sides of a chemical equation are equal. For example:
- Question 2:
What is a thermochemical equation? Give two examples.
Most chemical reactions are accompanied by either evolution or absorption of heat. These reactions are known as exothermic and endothermic reaction reactions respectively. Such an equation in which information about heat change is included is called a thermochemical equation. It is very important in such a case to indicate the physical sate of the various species involved
- Question 3:
Differentiate between an exothermic and endothermic reaction. Write one example for each of these reactions in the form of balanced chemical equation.
We know that constituent elements in a compound are bound by chemical bonds. During a chemical change, when bonds between the constituents of the reactants are broken, energy is consumed whereas energy is given out when the bonds are formed as in the case of products. Thus, depending on whether overall energy is given out or consumed, the reaction is either exothermic or endothermic.
Exothermic reactions: Chemical reactions in which energy is evolved (or given out) are known as exothermic reaction. For example: Formation of ammonia form nitrogen and hydrogen is an exothermic reaction. Endothermic Reaction: Reactions in which energy is absorbed are called endothermic reaction reactions. For example, When carbon reacts with sulphur , heat is absorbed during the process. Formation of nitric oxide (NO) is an endothermic reaction.
- Question 4:
Explain the following terms with examples in each case:
(i) Oxidation and (ii) Reduction.
(i) Oxidation: it us a process (a) in which oxygen or any electronegative element is added up or (b) hydrogen or any electropositive element is removed. Examples are:
(a)Sulphur burns in the air with a blue flame to form sulphur dioxide. Here oxygen is added up to sulphur. (b) Hydrogen sulphide combines with iodine to give hydrogen iodine and sulphur. (ii) Reduction: It is a process in which (a) Hydrogen or an electropositive element is added up. (b) Oxygen or electronegative element is removed. Examples are:
(a)Hydrogen reacts with chlorine to form hydrogen chloride. (b)Copper oxide is reduce with hydrogen.
- Question 5:
What is a Redox reaction?
A chemical reaction in which one substance is oxidised and the other is reduced is called a redox reaction. All oxidation-reduction reactions are redox reaction. In a chemical reaction, a substance gets oxidised only when another substance is present, which gets reduced. Question 6:
Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
When an iron nail is dipped in copper sulphate solution, it becomes brownish in colour and colour of copper sulphate fades due to the following reaction: In this reaction iron has replaced copper from its solution. Thus, amount of copper sulphate decreases and its colour fades.
- Question 7:
Why is respiration considered an exothermic reaction? Explain.
During digestion, food is broken down into simpler substances. Food like rice, potato and bread are made up of carbohydrates. These carbohydrates are further broken down into glucose. Glucose during respiration (inhalation of oxygen) is oxidised with the liberation of energy as shown below: Thus, respiration is an exothermic process.