Question

Fill in the blanks using the words given in the box.​

ignition, petrol, combustion, calorific value, combustible, inflammable​

(a) A chemical process in which a substance reacts with oxygen to give off heat is called ______.​
(b) Wood, paper, CNG are __________ substances.
(c) The lowest temperature at which a substance catches fire is called its ______ temperature.​
(d) Ignition temperature of _______ is lower than that of wood.
(e) The substances which have very low _______ temperature and can easily catch fire with a flame are called _______ substances.
(f) The amount of heat energy produced on complete combustion of 1kg of a fuel is called its ______.

Answer 1

(a) A chemical process in which a substance reacts with oxygen to give off heat is called combustion. Such type of substances are called combustible substances.
(b) Wood, paper and CNG combustible substances. The​

substances that undergoes combustion are said to be combustible. They are also called as fuels.​

(c) The lowest temperature at which a substance catches fire is called its ignition temperature. Different substances catches fire at different temperatures. For example, wood catches fire at 260°C whereas a wax catches fire at 300°C. ​

(d) The lowest temperature at which a substance catches fire is called its ignition temperature. The ignition temperature of petrol is lower than that of wood. Therefore, petrol catches fire easily than wood.​

(e) The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances. Petrol, diesel, etc. are the examples of such substances.​

(f) The amount of heat energy produced on complete combustion of 1kg of a fuel is called its calorific value. The calorific value of a fuel is expressed in a unit called kilojoule per kg (kJ/ kg).​