Changes Around Us: Physical and Chemical

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A physical change is one in which a substance undergoes a change in its physical properties (like shape, size, or state) but no new substance is formed. Examples: melting ice, folding paper, inflating…

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A chemical change is one in which one or more new substances are formed through a chemical reaction. The original substance cannot be easily recovered. Examples: burning wood, rusting iron, curdling m…

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The lime water turns milky because carbon dioxide from exhaled air reacts with lime water to form calcium carbonate (a white substance) and water. This is a chemical change as a new substance is forme…

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When vinegar and baking soda are mixed, they react to produce carbon dioxide gas (seen as fizzing and bubbles), water, and other substances. This is a chemical change because new substances are formed…

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Combustion is a chemical reaction in which a substance reacts with oxygen and produces heat and/or light. Example: burning of magnesium ribbon produces magnesium oxide, heat, and light.

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The three requirements for combustion are: 1) A combustible substance (fuel), 2) Oxygen, and 3) Heat to reach the ignition temperature. These form the fire triangle.

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Ignition temperature is the minimum temperature at which a substance catches fire. For example, when sunlight is focused on paper using a magnifying glass, it heats the paper until it reaches its igni…

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The candle stops burning because the glass tumbler cuts off the supply of oxygen, which is essential for combustion. Without continuous oxygen supply, the flame gets extinguished.