4.1 What leads to the formation of new substances during chemical reactions?
4.2 Do you agree with the following statements? Justify your answers.
(a) A change can be either physical or chemical but can never be both.
(b) All kinds of changes involve chemical reactions.
Answer (2)
The formation of new substances in chemical reactions happens through the rearrangement of atoms to create different products. I disagree with the notion that changes cannot be both physical and chemical or that all changes involve chemical reactions, as many changes are purely physical and do not alter the chemical structure of the substances involved.
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4.1 New substances are formed during chemical reactions due to the breaking of bonds in the reactants and the formation of new bonds in the products. When reactant molecules interact, their atomic arrangements change, leading to the creation of new substances with distinct physical and chemical properties. This process often involves energy changes, such as the release or absorption of heat.
4.2 Let's examine the statements:
(a) A change can be either physical or chemical but can never be both.
This statement is generally true . Physical changes involve changes in the state or appearance of a substance without altering its chemical composition (e.g., ice melting into water). Chemical changes involve the transformation of substances into new substances with different compositions and properties (e.g., rusting of iron). However, some processes might involve both, such as burning a candle, where the wax melts (physical) and burns (chemical).
(b) All kinds of changes involve chemical reactions.
This statement is false . Not all changes involve chemical reactions. Physical changes, such as melting, freezing, condensation, or evaporation, occur without any alteration in the chemical identity of the substances involved. Only chemical changes involve a chemical reaction where new substances are produced.
