Chemistry Basics

What is the definition of an element?

• An element is a type of atom.

• An element is a compound made up of multiple substances.

• An element is a substance that cannot be broken down into simpler substances by chemical means.

• An element is a form of energy.

Answer explanation

The question asks for the definition of an element. The correct answer is that an element is a substance that cannot be broken down into simpler substances by chemical means. This is because elements are the simplest form of matter and cannot be broken down further by ordinary chemical reactions. The other options are incorrect as they do not accurately define what an element is.

What is the definition of a compound?

• A compound is a substance formed by the physical combination of two or more elements.

• A compound is a substance formed by the biological combination of two or more elements.

• A compound is a substance formed by the chemical combination of two or more elements in definite proportions.

• A compound is a substance formed by the mechanical combination of two or more elements.

Answer explanation

The question asks for the definition of a compound. The correct answer is that a compound is a substance formed by the chemical combination of two or more elements in definite proportions. This distinguishes it from substances formed by physical, biological, or mechanical combinations, which are not considered compounds in the strict sense.

Give an example of an element.

• nitrogen

• oxygen

• hydrogen

• carbon

Answer explanation

The question asks for an example of an element. Elements are pure substances that cannot be broken down into simpler substances by chemical means. Oxygen, which is the correct answer, is one such element. It is a gas that makes up about 21% of the Earth's atmosphere and is essential for most forms of life.

Give an example of a compound.

• Water (H2O)

• Carbon dioxide (CO2)

• Oxygen (O2)

• Nitrogen (N2)

Answer explanation

The question asks for an example of a compound. A compound is a substance formed when two or more chemical elements are chemically bonded together. In the given options, Water (H2O) and Carbon dioxide (CO2) are compounds because they consist of more than one element. Oxygen (O2) and Nitrogen (N2) are not compounds but elements. The correct answer is Water (H2O), which is a compound made up of two Hydrogen atoms and one Oxygen atom.

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What is the difference between an element and a compound?

• An element is a substance made up of two or more different compounds, while a compound is a pure substance made up of only one type of atom.

• An element is a mixture of different substances, while a compound is a pure substance.

• An element is a substance made up of two or more different elements chemically combined, while a compound is a pure substance made up of only one type of atom.

• An element is a pure substance made up of only one type of atom, while a compound is a substance made up of two or more different elements chemically combined.

Answer explanation

The question asks about the difference between an element and a compound. The correct answer is that an element is a pure substance made up of only one type of atom, while a compound is a substance made up of two or more different elements chemically combined. This means that elements are simpler than compounds as they consist of a single type of atom, whereas compounds are formed by the chemical combination of two or more elements.

What is a chemical change?

• A chemical change is a process that results in the formation of new substances with no change in chemical properties.

• A chemical change is a process that results in the formation of new substances with physical properties.

• A chemical change is a process that results in the formation of new substances with the same chemical properties.

• A chemical change is a process that results in the formation of new substances with different chemical properties.

Answer explanation

The question asks about the nature of a chemical change. The correct answer is that a chemical change results in the formation of new substances with different chemical properties. This means that the substances formed after the change have different chemical properties than the original substances, indicating a chemical change has occurred.

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What is a physical change?

• A physical change is a change in the form or state of matter without any change in its chemical composition.

• A physical change is a change in the density of matter.

• A physical change is a change in the temperature of matter.

• A physical change is a change in the color of matter.

Answer explanation

The question asks about the definition of a physical change. The correct answer is that a physical change is a change in the form or state of matter without any change in its chemical composition. This means that the substance remains the same, only its physical appearance or state (solid, liquid, gas) changes. Other options mentioned changes in density, temperature, or color, which can be part of a physical change but do not define it.

Give an example of a chemical change.

• Burning of wood

• Cutting a piece of paper

• Mixing of salt and water

• Melting of ice

Answer explanation

The question asks for an example of a chemical change. A chemical change involves a chemical reaction, with new substances produced as a result of the change. Burning of wood is a chemical change because it involves a reaction with oxygen and produces ash, heat, light, and gases. Other options like cutting a piece of paper, mixing salt and water, or melting ice are physical changes, not chemical.

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Give an example of a physical change.

• Melting ice into water

• Boiling water into steam

• Burning wood into ash

• Mixing salt and water

Answer explanation

The question asks for an example of a physical change. A physical change is a type of change in which the form of matter is altered but one substance is not transformed into another. The answer, 'Melting ice into water', is a perfect example of this as the ice changes its state from solid to liquid, but it's still water.

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

• Chemical changes involve a change in temperature, while physical changes do not.

• Chemical changes can be reversed, while physical changes cannot.

• Chemical changes always produce a gas, while physical changes do not.

• Chemical changes involve a rearrangement of atoms and the formation of new substances, while physical changes only affect the physical properties of a substance.

Answer explanation

In a chemical change, atoms rearrange and form new substances, whereas a physical change only affects a substance's physical properties without altering its chemical composition. The other options are incorrect because they mention temperature, reversibility, or gas production, which are not definitive indicators to distinguish between chemical and physical changes.