6.1 Physical & Chemical Changes (Cambridge (CIE) O Level Chemistry): Flashcards
Exam code: 5070
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What is a physical change?
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What is a physical change?
A physical change is one in which no new chemical substances are formed. These changes are usually easy to reverse. Examples include melting, evaporating, and dissolving.
True or False?
Dissolving salt in water is a chemical change because the salt disappears.
False.
Dissolving is a physical change because no new chemical substances are formed. The salt can be recovered by evaporating the water.
What is a chemical change?
A chemical change is one in which new chemical substances are formed that have different properties from the reactants. Chemical changes are usually difficult to reverse.
Three observations that may indicate a chemical change has taken place are:
A ______ change
Formation of a ______
Production of ______
Three observations that may indicate a chemical change has taken place are:
A colour change
Formation of a precipitate
Production of gas
Why are chemical changes generally much harder to reverse than physical changes?
In a chemical change, new substances with different properties are formed from the reactants. To reverse the change, those new substances would need to be converted back into the original reactants, which typically requires a separate chemical reaction.
A chemical change produces new ______ with different ______ from the reactants. A physical change can usually be ______.
A chemical change produces new substances with different properties from the reactants. A physical change can usually be reversed.
True or False?
The majority of chemical reactions are exothermic.
True.
Most chemical reactions transfer thermal energy to the surroundings, causing a temperature rise. Only a small number of chemical reactions are endothermic.
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