How are chemical changes different from physical changes? (1 point)
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a They are reversible.
b They form new substances.
c They include shifts in the phase of matter d They involve heat.
b They form new substances.
The correct answer is b) They form new substances.
Chemical changes differ from physical changes because they result in the formation of new substances. During a chemical change, the atoms rearrange themselves to form different molecules or compounds. This change is usually accompanied by the breaking of chemical bonds and the formation of new ones. In contrast, physical changes do not involve the formation of new substances; instead, they only affect the physical properties of a substance, such as its appearance, state (solid, liquid, gas), or size, without altering its chemical composition. Reversibility (a), shifts in the phase of matter (c), and involvement of heat (d) can occur in both physical and chemical changes and are not exclusive to either type.
To understand how chemical changes are different from physical changes, let's look at the options provided.
a) They are reversible: This is not a characteristic that is specific to chemical changes. Both physical and chemical changes can be reversible or irreversible, depending on the circumstances. For example, the melting and freezing of ice is a reversible physical change, while burning wood is an irreversible chemical change.
b) They form new substances: This is one key difference between chemical and physical changes. Chemical changes result in the formation of new substances with different properties from the original substances. In a chemical change, bonds between atoms are broken and atoms rearrange themselves to form new molecules. For example, when hydrogen gas (H2) reacts with oxygen gas (O2) in the presence of heat, water (H2O) is formed, which is a completely different substance.
c) They include shifts in the phase of matter: This is a characteristic that can be seen in physical changes, not necessarily in chemical changes. Physical changes involve a change in the physical properties of a substance, such as changes in shape, size, or state of matter (solid, liquid, gas). Examples of physical changes include melting, freezing, boiling, or dissolving a substance.
d) They involve heat: Both chemical and physical changes can involve heat. Heat can be released or absorbed during both types of changes. For example, burning wood releases heat (an exothermic chemical change), while melting ice absorbs heat (an endothermic physical change).
Therefore, the correct answer is b) They form new substances, which is a characteristic specific to chemical changes.