Changes Around Us Class 6

Changes Around Us

a) Changes in substances refer to the different ways that materials can transform or alter.
b) These changes can involve various characteristics of the substances, such as physical properties (e.g., colour, shape, size, state of matter, temperature) or chemical properties (e.g., reactivity, composition, stability).
c) Changes in substances can occur through a variety of processes or factors, including:

1. Heating: When you heat something, like a piece of ice, it can change from a solid to a liquid (water). Similarly, if you heat water, it can change from a liquid to a gas (steam). So, heating can make substances change their form.

2. Applying force: When you apply force to something, like squeezing a sponge, it changes its shape. The sponge gets compressed or squished. This is an example of a physical change.

3. Mixing with other substances: When you mix different substances together, they can react and create new substances. For instance, when you mix vinegar and baking soda, they create a fizzing reaction and release carbon dioxide gas. This is a chemical change because new substances (carbon dioxide and water) are formed.

4. Environmental factors: Substances can also change due to environmental factors. For example, when iron is exposed to moisture and air for a long time, it can rust and turn reddish-brown. This is a chemical change caused by the reaction of iron with oxygen and water.

Different Types of Changes

Changes are generally of two types:

• Reversible Changes and
• Irreversible Changes

Reversible and irreversible changes are fundamental concepts in understanding how materials and substances interact with their environment.

Reversible Changes are those that can be undone, returning the substance to its original state. Examples include melting ice into water, which can be refrozen, or stretching a rubber band, which returns to its original shape when released.

Irreversible Changes permanently alter the substance, making it impossible to revert to its original form. Examples include burning wood, which turns into ash and cannot become wood again, or cooking an egg, which cannot be uncooked.

Physical and Chemical Changes

Periodic and Non-periodic Change

Exothermic and Endothermic Change

Change in Size due to Expansion and Contraction

a) When we heat a substance, its particles start moving faster and spread out. This makes the substance expand or become larger.
b) When we cool a substance, its particles slow down and come closer together. This makes the substance contract or become smaller.
c) Different materials can expand or contract by different amounts when heated or cooled.
d) Example: When the temperature increases, the liquid mercury inside a thermometer expands. This causes the mercury level to rise and gives a higher reading. When the temperature decreases, the mercury contracts and the level falls, giving a lower reading on the thermometer.
e) It's important to note that liquids also expand when heated, similar to solids.

Understanding how substances expand or contract with changes in temperature helps us explain various phenomena, such as the functioning of thermometers and the behaviour of different materials when heated or cooled.

Change of State on Heating

When we heat different substances, they can undergo changes in their state (solid, liquid, or gas). Some different processes involved are:

1. Melting:When a solid is heated, it can change into a liquid state. This process is called melting.
Example: When you heat ice, it melts and turns into liquid water.

2. Evaporation: When a liquid is heated, it can change into a gas state. This process is called evaporation.
Example: When you heat water, it evaporates and turns into water vapour (an invisible gas).

3. Condensation: When a gas is cooled, it can change into a liquid state. This process is called condensation.
Example: When water vapour in the air cools down, it condenses and forms water droplets, leading to the formation of clouds or dew.

4. Sublimation: Some solids can directly change into a gas state without going through the liquid state. This process is called sublimation.
Example: When solid dry ice (frozen carbon dioxide) is heated, it directly changes into carbon dioxide gas without becoming a liquid.

Anomalous Expansion of Water

a) When most substances are cooled, they contract and become smaller in volume. However, water behaves differently.
b) When water is cooled from higher temperatures, it follows normal behaviour and contracts, just like other substances.
c) However, when it gets colder than 4°C, something different happens. Instead of contracting, water starts to expand and takes up more space.
d) This means that when water freezes and turns into ice, it actually becomes less dense than liquid water. That's why ice can float on top of the water.
e) Scientists call this unusual behaviour the "anomalous expansion of water."
f) The anomalous expansion of water is important for life in rivers and lakes. When it gets really cold, the top layer of water freezes and forms ice. This ice acts as a protective layer, keeping the water underneath warmer and allowing plants and animals to survive.

Frequently Asked Questions

1. What are natural changes in the environment?

Seasons, climatic changes and natural disasters like earthquakes and volcanic eruptions are examples of how the environment changes naturally.

2. What is climate change, and how does it affect us?

Permanent changes to temperature and weather patterns are referred to as climate change. It may result in extreme changes in the weather, elevated sea levels, and ecological disturbances that impact plant and animal life.

3. What are the examples of endothermic change?

Here are some examples of endothermic change:

1. Melting Ice: Imagine taking an ice cube from the freezer. As it turns into the water in your hand, it's absorbing heat from the environment. This is an endothermic change.

2. Baking Cookies: When you help in baking cookies at home, the dough transforms into delicious cookies in the oven. This process is endothermic as it absorbs heat during the baking.

3. Photosynthesis in Plants: In science class, you learn about photosynthesis in plants. This is an endothermic process where plants absorb sunlight to make their own food.

4. Cooling Effect of Evaporation: On a hot day, sweating helps cool your body. The water on your skin evaporates, taking in heat from your body, providing a refreshing sensation. This is an endothermic change.

5. Using an Instant Cold Pack: If you've ever used an instant cold pack for a bump or bruise, you're witnessing an endothermic change. The chemicals inside the pack absorb heat, creating a cold sensation.

6. Dissolving Salt in Water: During a science experiment, when you dissolve salt in water, the process is endothermic. The salt absorbs heat from its surroundings to dissolve in the water.

4. What are the examples of periodic and non-periodic changes?

Here are some examples of periodic and non-periodic changes:

Examples of Periodic Changes

1. Day and Night Cycle: The rotation of the Earth leads to a consistent pattern of day and night, making it a periodic change.

2. Seasonal Changes: The Earth's orbit around the Sun causes seasonal variations, with cycles of spring, summer, autumn, and winter representing periodic changes.

3. Moon Phases: The changing appearance of the moon in the night sky, from full moon to new moon and back, is a periodic change driven by the moon's orbit around the Earth.

4. Tides: The rise and fall of ocean tides are periodic, influenced by the gravitational pull of the moon and the sun on Earth.

Examples of Non-Periodic Changes

1. Volcanic Eruptions: Volcanic eruptions are non-periodic, occurring irregularly based on geological conditions and build-up of pressure beneath the Earth's surface.

2. Earthquakes: Earthquakes are non-periodic events caused by the sudden release of energy in the Earth's crust, with no predictable cycle.

3. Forest Fires: Forest fires are non-periodic and typically result from a combination of dry conditions, human activities, and lightning strikes.

4. Meteorite Impacts: Meteorite impacts on Earth are non-periodic events that happen randomly when celestial bodies collide with our planet.

5. What is the role of technology in bringing about changes in our daily lives?

Technology plays an important role in shaping our daily lives by introducing innovations, improving communication, and contributing to advancements in various fields such as medicine, education, and transportation.