Chemical Reaction // Class 9 Science Notes

                      Chemical Reaction

Class 9 Science Chapter 15

* Short Answer type questions:

a. What are reactants and products?

 → Reactants are those substances that undergo chemical change during during a chemical reaction. 

→ Products are those substances, which are formed as a result of chemical change in the reactants.. 

b. What is a balanced chemical equation? 

→ The chemical equation, in which the total number at atoms in reactants and products is equal is is called equation a balanced chemical

c. Write down the balanced chemical equation of the reaction between zinc and hydrochloric acid. What type of chemical reaction.

= Zine + Hydrochloric acid =Zinc chloride + Hydrogen 

Zn + HCl Zn + 2HCl2 in this? >ZnCI2 + H2

→ ZnCl₂ +H₂ 

This type of chemical reaction is single displacement reaction.

d. What endothermic reaction?

 → The chemical reaction which Occurs by the absorption of heat from the surroundings is called endothermic reaction.

e. What is a Formula equation? 

= The chemical equation which is written in terms of molecular Formulae is called Formula equation.

f.  What is the meaning of '+' between the reactant and 'A' above the arrow head in a chemical. equation?

=The meaning above the '+' between the reactant and 'A' head in a chemical equation is............Sorry!

2. Long answer type questions: 

a. What is a chemical reaction? In how many ways. can chemical reactions take place? 

= The process by which a chemical changes takes place is called a chemical reaction.

b. Enlist any four examples of chemical change.

→ The four examples at chemical change are:

i. Changing milk into curd.

ii. Rusting of iron

iii. Cooking of food

iv. burning of wood.

c. What do you mean by a diatomic element? Give any four examples.

= A diatomic element is an element which have two atoms in the molecules. ex: hydrogen, nitrogen oxygen, Fluorine, etc..

d. List out the information that can be obtained From a balanced chemical equation?

 →The information that can be obtained from a balanced chemical equation are: 

i. The reactants and products through their symbols and formulae. 

ii. The ratio of molecules of reactants and products. 

iii. If the mass are expressed in grams then the equation also gives the molecular ratio it reactants and products.

 iv. Type of chemical reaction. 

v. Names of reactants and products.

e. Enlist the limitation of a balanced chemical reaction.

= The limitation of a balanced chemical reaction are:

i. Chemical equations cannot tell the physical state and concentration of reactants and the state of products

ii. It does not give any information about the rate of chemical reaction and the time taken by the reaction to complete.

 iii. It does not state wheather the reaction occurs by itself or certain conditions like heat, light and catalyst are required. 

iv. It does not show that the reaction is either explosive or not.

v. It does not tell that chemical reaction will start immediately or it will take time to be started. 

f. What would be the exothermic and endothermic reactions while Sanjay is cooking rice on a Firewood stove?

→ While Sanjay is cooking rice on a Firewood stove, Cooking of rice is endothermic reaction because, cooked rice cannot be made tice back and tice absorbs heat from the external sources and utilizes for its cooking and firewood stove. is exothermic reaction.                                               

g. When you touch outside the beaker containing two chemicals reacting together, you feel had hot. What type of chemical reaction is going the beaker? Explain with an example. 

→When we touch outside the beaker containing two chemicals reacting together, we feel hot, this type it reaction is exothermic chemical reaction .ex :Calcium chloride produces. Lar releases heat to the water when it reacts with water.

h. Are chemical reactions important to life. Explain?

 → Chemical reactions are important to life because in everywhere place chemical reaction. caused. Chemical reactions are needed to digest Food. It is important for plants to grow. I enables us to store energy is needed. In everywhere chemical body while breathing, while taking a shower, Cocking, etc.

i. Mention the steps of the method at writing a balanced chemical equation with an example 

= 1. First write the correct word equation to express the actual chemical reaction 

2. Write the molecular formulae at all the reactants and products correctly, express the ward equation in the Formula chemical equation. 

3 Separate the reactants and the products by the sign of an arrow. It reactants or products are more than one, connect them by a sign of plus (+).

 4. Balance 0 and H atoms used at many places in the equation at last 

5. For balancing, the number should be added as co-efficient . i.e: in the front of the molecules.

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