Effects of Chemical
We know that every chemical reaction
requires a specific condition to occur. When chemical reactions take place
there will be production of heat, light, sound, pressure etc. and also many
1. Biological Effects
a. Spoilage of food
Food spoilage may be defined as any
change that causes food unfit for human consumption. The chemical reactions
catalysed by the enzymes result in the degradation of food quality in the form
of development of bad tastes and odour, deterioration and loss of nutrients.
* Rotten eggs develop a bad smell
due to formation of hydrogen sulphide gas.
* Decaying of vegetables and fruits
due to microbes.
b. Rancidity of fishes
Fishes and meat containing high
levels of poly unsaturated fatty acids undergo oxidation. It causes bad odour
when exposed to air or light. This process is called rancidity.
c. Apples and fruits
turn brown when cut
Apples and some fruits turn brown
due to chemical reaction with oxygen in air. This chemical reaction is called
browning. The cells of apples, fruits and other vegetables contain an enzyme
called polyphenol oxidase or tyrosinase. When in contact with oxygen it
catalyses a biochemical reaction in which the phenolic compounds present in
plants become a brown pigment known as melanins.
2. Environmental Effects
Our environment provides air to
breathe, water to drink and the land to produce food. Due to industrial processes
and increasing number of automobiles, our environment is badly affected
now-a-days. So, there is an unwanted change in the physical, chemical and
biological properties of the environment. This is termed as pollution. The
substances which cause these changes are called pollutants. Generally there are
three types of pollutions vizair, water and land pollution. Due to increasing
human activities, lot of chemical substances are produced artificially which
harm all the living and non living things. The types of chemical substances and
their effects are given in table below (Table 10.1) .
What happens to the steel benches
and tables during rainy season? They turn into reddish brown. Isn’t it? Do you
know why? This is because when the iron metal come into contact with water and
oxygen, it undergoes a chemical reaction called rusting.
c. Tarnishing of metal
Shiny metal surfaces and other
articles lose their shining appearance due to chemical reactions on the
surface. For example, silver articles become black when exposed to atmospheric
air. Similarly, brass vessels which contain copper as one of the constituents
develop a greenish layer when exposed to air for a long time. This is due to a
chemical reaction between copper and moist air to form basic copper carbonate
and copper hydroxide.
3. Production of Heat,
Light, Sound and Pressure
a. Production of Heat
Have you ever rubbed your palms in
winter season to keep yourself warm? Have you noticed the heat produced when
you use cycle pump? Similarly some chemical reactions produce heat energy also.
Such reactions are called exothermic
reactions. For example, when you add water to quicklime (calcium oxide),
lot of heat is released to produce slaked lime (calcium hydroxide).
Take two clean test
tubes. Take sulphuric acid in one test tube and a solution of sodium hydroxide
in another tube. Slowly and carefully add sodium hydroxide solution to
sulphuric acid. Touch the sides of test tube. What do you feel? What do you
b. Production of Light
When you ignite a candle, you get
light as a result of burning. Some chemical reactions produce light. For
example, when a piece of magnesium ribbon is burnt in a flame, bright light is
produced with heat. Even the fireworks used during festival times produce
different coloured lights which are all due to chemical reactions.
c. Production of Sound
When we speak sound is produced. When
you hit metals like iron, copper etc. , a sound is heard. Some chemical
reactions do produce sound when they take place. What happens when you fire
crackers during Deepavali? The chemical substances present in the crackers
undergo some chemical reactions to produce sound.
Take a clean test
tube. Add some dilute hydrochloric acid. Drop a piece of magnesium or a piece
of zinc metal. What do you see? Now bring a burning match stick near the mouth
of the test tube. What do you hear? What do you infer?
You can hear a pop sound. When metals
like zinc or magnesium reacts with dilute acids hydrogen gas is produced. Since
hydrogen gas is highly flammable it reacts with oxygen present in air to
produce pop sound.
d. Production of
When you compress hard a balloon
having full of air, it will burst. This is due to sudden release of air from
the balloon as a result of increased pressure on compression. Some chemical
reactions produce gases which increases the pressure when the reaction takes
place in a closed container. If the pressure level goes beyond the limit, we
get the explosion. Explosives and fireworks burst because of this reason. When
they are ignited they explode due to pressure generated by gases from the
chemical reactions. Thus, you hear a huge sound.