Changes Around Us

A change in a substance means that one or more of its properties, such as state, size, shape, color, smell, temperature, composition, or structure, have altered. For instance, when ice melts into water, it undergoes a change in state from solid to liquid. This change is brought about by a change in the property of temperature.

The melting of ice into water and the drying of clothes both involve changes in state. Melting ice requires the input of heat, demonstrating that heat is the 'cause' that leads to the 'effect' of ice changing into liquid water. Similarly, the drying of clothes is caused by the evaporation of water, which occurs when heat is applied to the wet clothes, driving the water molecules into the air.

This statement implies that changes in substances require an external influence or 'cause' to trigger them. For example, the ripening of a fruit is caused by internal chemical processes and the influence of time and temperature. These processes wouldn't occur without the 'cause' of the fruit being exposed to the right conditions.

<p>The burning of fuels involves a rapid chemical reaction with oxygen, releasing heat and light. This change is caused by the presence of a fuel source and a source of ignition. Rusting of iron, however, is a slow chemical reaction involving the oxidation of iron in the presence of moisture and oxygen. It is caused by the prolonged exposure of iron to these elements.</p> Signup and view all the answers

<p>The burning of fuels and the rusting of iron involve changes in the composition of the substances. In the burning of fuels, the fuel reacts with oxygen, creating new substances like carbon dioxide and water vapor. Rusting involves the formation of iron oxide, a new substance with different properties than pure iron. These changes are considered more significant because they result in the creation of entirely new substances with distinct chemical properties, unlike changes in state which simply alter the physical form of the substance.</p> Signup and view all the answers

<p>A permanent alteration in the substance's properties</p> Signup and view all the answers

<p>The change of milk into curd can be prevented by maintaining a low temperature. Curdling is caused by bacteria that thrive in warm conditions. By keeping the milk refrigerated, we can prevent the bacteria from multiplying and causing the change in the milk's properties.</p> Signup and view all the answers

<p>Formation of curd from milk</p> Signup and view all the answers

<p>Cause and effect principle</p> Signup and view all the answers

<p>Melting of ice</p> Signup and view all the answers

<p>Cause</p> Signup and view all the answers

<p>Burning of fuels</p> Signup and view all the answers