Grade 9 Chemistry, Lesson 3 - Physical and Chemical Properties and Changes

Summary

This chemistry lesson explores the distinction between physical and chemical properties and changes. Physical properties, such as state of matter, color, and density, can be measured without altering a substance. Chemical properties, however, require a reaction to be observed. The video clarifies this by contrasting physical changes, like cutting bread or turning on a light, with chemical changes, such as baking bread or frying an egg, which result in new substances. It also discusses how to identify chemical changes through color changes, heat production, and irreversibility.

Takeaways

• 🧪 Physical properties are characteristics of substances that can be measured without changing the substance's identity, such as state of matter, color, density, and hardness.
• 🔨 Hardness is the resistance of a solid to being scratched or dented, as illustrated by the scratches on a canoe from rocks.
• 🛠 Malleability refers to how easily a substance can be hammered or bent into different shapes, with metals and Play-Doh being examples of malleable substances.
• 🧵 Ductility is the ability of a substance to be pulled into wires without breaking, as demonstrated by stretching aluminum.
• 💧 Solubility is a physical property that describes a substance's ability to dissolve in a solvent, like salt dissolving in water.
• 🍯 Viscosity is a measure of a liquid's resistance to flow, with honey being an example of a highly viscous substance.
• 🔥 Chemical properties describe a substance's potential to react chemically with other substances to form new compounds, and they can only be observed through chemical reactions.
• 🔥 Combustibility and flammability are chemical properties that indicate a substance's ability to react quickly with oxygen, producing heat and light, such as catching on fire.
• 🌡 Acidic or basic properties are also chemical properties that define how a substance reacts with other chemicals.
• 🥚 Chemical changes involve the creation of a new substance, such as the reaction of hydrogen and oxygen to form water (H2O).
• 🧊 Physical changes do not result in the creation of a new substance, but may involve a change in state, like water turning into ice.

Q & A

What are physical properties?

Physical properties are characteristics of substances that can be measured or observed without changing the composition of the substance. Examples include state of matter, boiling and melting points, color, luster, density, hardness, malleability, ductility, and solubility.

What is the difference between hardness and malleability?

Hardness is the resistance of a solid to being scratched or dented, while malleability describes how easily a substance can be hammered or bent into different shapes.

Can you give an example of a physical property that demonstrates ductility?

An example of ductility is a tube of aluminum, which can be stretched out into a longer, thinner version without snapping.

What is solubility in the context of physical properties?

Solubility is the ability of a substance to dissolve in a solvent, such as salt dissolving in water.

How does viscosity relate to the flow of a liquid?

Viscosity of a substance describes how quickly it flows in its liquid form. A higher viscosity indicates a slower flow, like honey pouring slowly over a plate.

What are chemical properties?

Chemical properties describe the ability of a substance to chemically react with another substance to produce a new chemical. They can only be observed through a chemical reaction.

What are some examples of chemical properties?

Examples of chemical properties include combustibility (ability to react with oxygen and produce heat and light) and acidity or basicity, which describe reactions with other chemicals.

How can you distinguish between a chemical change and a physical change?

A chemical change involves the creation of a new substance, while a physical change involves a change in state or appearance without the formation of a new substance.

What are some indicators that a chemical change has occurred?

Indicators of a chemical change include the appearance of a new color, the release of heat or light, the formation of gas bubbles, the creation of a precipitate when two liquids are mixed, and the difficulty of reversing the change.

Can you provide an example of a chemical change from the script?

An example of a chemical change from the script is baking a loaf of bread, which is hard to reverse and involves a color change.

What is the difference between turning on a light bulb and frying an egg in terms of physical and chemical changes?

Turning on a light bulb is a physical change because it can be easily reversed and does not involve the creation of a new substance, while frying an egg is a chemical change due to the color change and the difficulty of reversing the process.