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Which statement is correct regarding physical and chemical changes?
Physical changes form new substances
All physical changes are irreversible
All changes in solutions are chemical
Chemical changes alter composition
Chemical changes alter composition
Chemical changes involve the transformation of substances into entirely new materials with different chemical properties by rearranging atoms. Physical changes only alter the state, size, or shape of a substance without changing its internal chemical identity.
Chemical changes involve the transformation of substances into entirely new materials with different chemical properties by rearranging atoms. Physical changes only alter the state, size, or shape of a substance without changing its internal chemical identity.
Think of a physical change like tearing a sheet of paper (it's still paper); a chemical change is like burning that paper into ash and smoke (it's no longer paper).
CP-NC: Chemical changes Produce New Composition.
A+BтЖТC+D тАФ represents a general chemical reaction where reactants yield new products.
╬ФH=HproductsтАЛтИТHreactantsтАЛ тАФ represents the enthalpy change during a chemical process.
In a chemical change, old chemical bonds are broken and new ones are formed, leading to a change in the molecular structure. This is often accompanied by energy changes, such as the release or absorption of heat (Q=╬ФH), light, or gas evolution. In contrast, physical changes involve only intermolecular forces, such as the energy required to overcome hydrogen bonding during phase transitions like melting or boiling.
Chemical changes involve making or breaking chemical bonds.
Physical changes are often reversible, whereas chemical changes are typically permanent.
Mass is conserved in chemical reactions according to the Law of Conservation of Mass.
New chemical substances are defined by their distinct properties (melting point, reactivity, etc.).
Digestion of food (chemical change)
Melting of ice (physical change)
| Feature | Physical Change | Chemical Change |
|---|---|---|
Substance Identity | Retained | Changed |
Reversibility | Usually reversible | Usually irreversible |
Option A is incorrect because physical changes do not form new substances.
Option B is incorrect because many physical changes, like dissolving salt in water, are technically reversible but some, like breaking a glass, are not; thus, not all are inherently reversible.
Option C is incorrect because dissolving a solute in a solvent is a physical change (the substance remains the same, just dispersed).
D is correct тАФ Chemical changes result in the formation of new substances due to a permanent alteration in chemical composition.
If you see bubbles, color change, or temperature change without heating, it is a strong indicator of a chemical change!
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