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QuestionChemistry

Explain the following statement: "Dissolving sugar in water is a physical change, but heating sugar to form caramel is a chemical change."
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Step 1:
I'll solve this problem by explaining the key differences between physical and chemical changes using the example of sugar.

Step 2:
: Define Physical Change

- The sugar (sucrose, $$C_{12}H_{22}O_{11}$$) maintains its original molecular structure
A physical change is a transformation that alters the physical properties of a substance without changing its chemical composition. In the case of dissolving sugar in water: - Only the physical state changes (from solid to dissolved) - No new chemical bonds are formed - The sugar can be recovered by evaporating the water - Properties like chemical identity remain unchanged

Step 3:
: Characteristics of Sugar Dissolution

- The molecular formula $$C_{12}H_{22}O_{11}$$ remains intact
When sugar dissolves in water: - Sugar molecules separate and distribute throughout the water - No chemical bonds are broken or created - This is a reversible process - Only physical properties like concentration change

Step 4:
: Define Chemical Change

- Complex molecules like $$C_{12}H_{22}O_{11}$$ transform into different compounds
A chemical change involves the formation of new chemical substances with different molecular structures and properties. In caramelization: - Sugar molecules break down - New chemical bonds form - Process is irreversible - New substances with different properties emerge

Step 5:
: Caramelization Process

When sugar is heated: - Molecules begin to break down - Carbon-based compounds form - New molecules like hydroxymethylfurfural (HMF) are created - Color changes from white to brown - Chemical composition fundamentally alters

Final Answer

Dissolving sugar in water is a physical change because the sugar molecules remain chemically unchanged, while heating sugar to caramel is a chemical change because the molecular structure is fundamentally transformed, creating new chemical compounds.