a) Production of heat:
Chemical reactions produce heat energy. These reactions are called exothermic reactions. (ex) When water is added to quick lime, a lot of heat is produced.
b) Production light:
i. some chemical reactions produce light. (ex) when a piece of magnesium ribbon is burnt in a flame, bright light is produced with heat.
ii. Fireworks produce different colored lights due to a chemical reaction.
c) Production of sound:
i. some chemical reactions produce sound. (ex) Crackers produce sound by undergoing some chemical reactions.
ii. Hydrogen gas continues burning a match stick with a pop sound due to chemical reaction.
d) Production of pressure:
i. Some chemical reactions generate pressure.
ii. Some chemical reactions produce gases which build up pressure in a closed container.
iii. If the pressure level goes beyond the limit, we get the explosion.·
iv. (ex.) When explosives, fireworks are ignited, they explode due to the pressure generated by gases from the chemical reactions.
e) Evolution of gas:
i. In some chemical reactions. gases are evolved.
ii. (ex.) When dilute hydrochloric acid is added to a solution of sodium carbonate, carbon dioxide gas is evolved.
f) Change in color:
i. Some chemical reactions produce a change in color.
ii. (ex.) When an iron nail is placed in copper sulphate solution, the colour changes into green due to chemical reaction between iron and copper sulphate solution.

a) Environment is the place around us that comprises both living and non-living things.
i) Our environment provides air to breathe, water to drink and the land to produce food.
ii) Due to human activities like increasing industries, increasing number of automobiles, etc., a lot of chemical substances are produced artificially.
iii) So there is an unwanted change in physical, chemical and biological properties of the environment.
iv) This is termed as pollution.
v) This harms all the living and non-living things.
Types of pollution:

b) Rusting: when iron materials are exposed to air and water, they undergo a chemical reaction called rusting. This makes iron soft and weak.
c) Tarnishing: When silver objects are exposed to air, they undergo a chemical reaction and the colour changes to black. This is called tarnishing. When copper objects are exposed to air, they undergo a chemical reaction and the colour changes to green.

Biological effects:
a) Spoilage of food and Vegetables:
i. Food spoilage may be defined as any change that causes food unfit for human consumption.
ii. The chemical reactions catalysed by the enzymes result in the degradation of food quality.
iii. It develops bad tastes, odour, deterioration and loss of nutrients.
iv. (eg.) 1. Rotten eggs develop a bad smell due to the formation of hydrogen sulphide gas.
v. (eg.) 2. Decaying of vegetables and fruits due to microbes.
b) Rancidity of fishes and meat:
i. Fishes and meat contain high levels of polyunsaturated fatty acids.
ii. When exposed to air or light these polyunsaturated fatty acids undergo oxidation causing bad odour.
iii. This process is known as rancidity.
c) Apples and fruits turn brown when cut:
i. The cells of apples, fruits and other vegetables contain an enzyme called poly phenol oxidase or tyrosinase.
ii. This enzyme when comes in contact oxygen catalyses a biochemical reaction of plants phenolic compounds to brown pigments known as melanins.
iii. This chemical reaction is browning.

(i) Spoilage of food and vegetables:
Food spoilage may be defined as any change that causes food unfit for human consumption
The chemical reactions catalyzed by the enzymes result in the degradation of food quality such as development of bad tastes and odour, detorioration and loss of nutrients.
Eg: Rotten eggs develop a bad smell due to the formation of hydrogen sulphide gas.
Decaying of vegetables and fruits due to microbes.
(ii) Rancidity of fishes and meat:
Fishes and meat contains high levels of polyunsaturated fatty acids.
These fatty acids undergo oxidation when exposed to air or light.
It results in bad odour. This process is called rancidity.
(iii) Apples and fruits turn brown when cut:
It is due to chemical reaction with oxygen in air.
The cells of apples contain an enzyme called tyrosinase that when in contact with oxygen catalyses a biochemical reaction of plant's phenolic compounds to brown pigments known as melanins.

Rancidity is a condition in which the food items develop bad odour due to chemical reactions by microbes.

Chemical reactions carried out by heat are called thermolysis.

Chemical reactions carried out by light are called photolysis.

Chemical reactions carried out by electricity are called electrolysis

Rusting is a chemical reaction in which iron objects form hydrated ferric oxide in the presence of oxygen and water.

Carbon dioxide, carbon monoxide, oxides of sulphur, oxides of nitrogen, chloro fluoro carbons, methane etc

i. The reactions achieved by the supply of heat only are called thermolysis.
ii. When lead nitrate is decomposed by heating it gives brown coloured nitrogen dioxide gas.

i) Chemical reactions carried out by electricity are called electrolysis.
ii) Sodium chloride solution called brine solution is taken.
iii) When electric current is passed through brine solution, a chemical reaction occurs.
iv) Hydrogen gas, chlorine gas, and sodium hydroxide are formed as products.

i. When a solution of sodium chloride is mixed with a solution of silver nitrate the following chemical reaction occurs.
ii. Sodium chloride + Silver nitrate ⟶ Silver chloride + Sodium nitrate
iii. The product silver chloride appears as a white precipitate.

i. The head of a match stick contains potassium chlorate and antimony trisulphide.
ii. The sides of the matchbox contain red phosphorous.
iii. When a match stick is rubbed on the sides of a matchbox, the chemicals come in contact with each other. A chemical reaction occurs producing heat, light and smoke.