Question

Burning of wood is a _ _ _ _ _ change.
a.) reversible
b.) physical
c.) irreversible
d.) all of these

Answer 1

Hint: The burning of wood is a chemical change as when the wood is burnt. It changes into ashes and the chemical composition of ashes is different from the wood. Further, the ash formed once can not be converted into wood back. Such a change is not possible.

Complete step by step solution:
We will start with what is burning and what are the factors on which it depends.
So, the burning is the chemical process in which two or more atoms combine and release a large amount of energy. One of these molecules that combine is the oxygen and the other one is an oxidizer. The energy is released in the form of heat and light.
When the wood reacts with oxygen in the air to provide some activation energy, it burns to ash. The wood is to be heated to some temperature so that it could burn. This temperature is called the ignition temperature. As the wood heats up, it is a hydrocarbon. So, carbon atoms absorb energy and rise. This results in light.
Now, coming to the process, we are given options.
The first is reversible. The reversible process is the one in which products can be converted back to reactants. Say, for a reversible process
Reactants$\rightleftharpoons$Products
Another option is a physical change. A physical change occurs when there is a change in only physical properties of the products and the chemically the constituent remains the same. This is not the case here. The burning of wood into ash is a chemical change.
The third option is irreversible. The change in which the products formed can not be converted into reactants is the irreversible change.
The wood burns to give ash and this ash can not be returned back into the wood by any process. So, this process of burning of wood is irreversible in nature.

Thus, the option (C) is the correct answer.

Note: It must be noted that during physical change, only the physical properties of reactant and product are different. The chemical constituent of reactant and product will be the same only while in case of chemical change, the physical properties can be the same or different but the chemical structure will be different.