Question

Label each of the following as either a physical process or a (a) crushing a metal can, \((\mathbf{b})\) production chemical process: of urine in the kidneys, \((\mathbf{c})\) melting a piece of chocolate, \((\mathbf{d})\) burning fossil fuel, \((\mathbf{e})\) discharging a battery.

Short answer

a) Crushing a metal can: physical process b) Production of urine in the kidneys: chemical process c) Melting a piece of chocolate: physical process d) Burning fossil fuel: chemical process e) Discharging a battery: chemical process

Step-by-step solution

a) Crushing a metal can

Crushing a metal can is a physical process. When a metal can is crushed, its appearance and shape change, but the metal itself remains the same. No new substances are created during the process of crushing a metal can.

b) Production of urine in the kidneys

The production of urine in the kidneys is a chemical process. This is because various substances are filtered from the blood, such as water, salts, and waste products, which then form urine. As new substances are created during this process, this is considered a chemical process.

c) Melting a piece of chocolate

Melting chocolate is a physical process. When chocolate melts, it changes from a solid to a liquid state, but the composition of the chocolate remains the same. No new substances are created during the process of melting chocolate.

d) Burning fossil fuel

Burning fossil fuel is a chemical process. During combustion, the fossil fuel reacts with oxygen in the air to produce new substances, such as carbon dioxide, water vapor, and other byproducts. As new substances are created during this process, this is considered a chemical process.

e) Discharging a battery

Discharging a battery is a chemical process. As a battery discharges, a chemical reaction occurs inside the battery that converts chemical energy into electrical energy. The substances within the battery change during this reaction, resulting in the formation of new substances.

Key concepts

Physical Changes

Physical changes involve alterations in the form or appearance of a substance, without changing its chemical structure. A simple way to remember this is that the substance remains the same even if it looks different. For example, when you crush a metal can, you alter its shape but the metal itself doesn't change its nature. It is still the same material, just in a different shape.

Another example of a physical change is when chocolate melts. The chocolate changes from a solid to a liquid as temperature rises. Although the state changes, the actual composition stays the same, hence it is still chocolate, which implies no new substances are formed.

Physical changes are usually reversible, meaning the substance can return to its original state under the right conditions.

• Example 1: Crushing a metal can
• Example 2: Melting chocolate

Chemical Changes

Chemical changes are processes where a substance transforms into a new substance with different properties. This involves making or breaking chemical bonds, which leads to an entirely new set of compounds.

A classic instance of a chemical change is the production of urine in the kidneys. Here, components such as water, salts, and wastes are filtered and chemically recombined, forming a completely new substance, which is urine.

Chemical changes are often irreversible because they involve a fundamental change in the substance's makeup. For instance, when you burn fossil fuels, a chemical reaction with oxygen produces new substances like carbon dioxide and water vapor.

• Example 1: Production of urine in the kidneys
• Example 2: Burning fossil fuel

Combustion Reaction

A combustion reaction is a type of chemical change that typically involves the reaction of a substance with oxygen, resulting in the release of energy in the form of heat and light. Combustion is a common example of an exothermic reaction, meaning it releases energy.

When fossil fuels like coal, oil, or gas are burned, they undergo combustion. During this process, the fuels react with oxygen from the air to produce new substances, including carbon dioxide and water. This reaction is an important source of energy, powering engines and generating electricity.

Combustion reactions are crucial for modern life, but they also contribute to pollution and global warming due to the release of greenhouse gases.

• Produces energy
• Generates new substances
• Releases greenhouse gases

State of Matter Changes

Changes in the state of matter, such as melting, freezing, condensation, and evaporation, are classic examples of physical changes. Matter changes state based on temperature and pressure, but its chemical identity remains the same.

For instance, when a piece of chocolate melts, it transitions from a solid to a liquid. This shift happens because heat energy is absorbed, causing the molecules to move faster and spread apart. Despite the change in form, the substance remains chocolate.

State changes are reversible. If the melted chocolate cools, it can solidify back to its original form without any alteration in its chemical composition.

• Melting: solid to liquid
• Freezing: liquid to solid
• Evaporation: liquid to gas
• Condensation: gas to liquid