Question

State whether the following statements are true or false. If false, write the correct statement.
Desirable changes are meaningful, while undesirable changes are unfavourable.
(A) During physical changes the composition of the substance is not altered, but the properties of the original substance are altered.
(B) During a chemical change, the composition of the original substance is not altered & the change is irreversible.
(C) Melting of butter and wax are examples of chemical changes.
(D) Melting of ice is an exothermic, irreversible chemical change.

Answer 1

Hint: Reversible changes are those that can be reverted back to their original form again while irreversible changes are those that cannot be reverted back to their original form again. Reversible changes are also known as physical changes while irreversible changes are known as chemical changes.

Complete step by step solution
Desirable changes are meaningful, while undesirable changes are unfavourable – desirable changes are those that are desired to take place, i.e., we want them to take place while undesirable changes are those that occur without our intention. So the first statement is true.
During physical changes the composition of the substance is not altered, but the properties of the original substance is altered – this statement is true because during the melting of ice, which is a physical change, the formula of water does not change but volume and the temperature of ice which are its physical attributes changes.
During a chemical change, the composition of the original substance is not altered & the change is irreversible – During the chemical change, both the physical and the chemical properties of the substances changes and the changes is irreversible. Hence a part of the statement is incorrect and so this is False.
Melting of butter and wax are examples of chemical changes – Both these changes are examples of physical. Changes as on solidifying the butter and wax will again get them back to their original states. Hence this statement is False.
Melting of ice is an exothermic, irreversible chemical change – This Statement is incorrect because ice requires heat energy to melt away and so it is an endothermic change and also a physical change because it can again lose that heat energy to get solidified gain. So this is false.

Note
In a physical change, the form of a chemical substance is affected, but its chemical composition remains unaltered while in a chemical change, the chemical composition of the substance is altered completely to form a new substance.