Year 8 Science

What is a chemical property?

• A property that can be observed directly

• A property that describes how a substance combines with others to form new chemicals

• A property that involves a change of state

• A property that is always visible.

Answer explanation

A chemical property refers to how a substance interacts with others to form new substances. This distinguishes it from physical properties, which can be observed without changing the substance's identity.

Fill in the blank: During physical changes, no new substances are (a)   .

Answer explanation

During physical changes, the composition of substances remains the same, meaning no new substances are formed. This distinguishes physical changes from chemical changes, where new substances are created.

Explain the process of photosynthesis as a chemical reaction. (Open-ended question)

Answer explanation

Photosynthesis is a chemical reaction where plants convert carbon dioxide and water into glucose and oxygen using sunlight. The overall equation is 6CO2 + 6H2O + light energy -> C6H12O6 + 6O2.

Evaporation is a change of state from a liquid to a (a)   .

• Solid

• Gas

• Plasma

• Liquid

Answer explanation

Evaporation is the process where a liquid changes into a gas. This occurs when molecules at the surface of the liquid gain enough energy to overcome intermolecular forces and enter the gas phase, making 'Gas' the correct answer.

Fossil fuel + oxygen ⟶ (a)   + water.

Answer explanation

When fossil fuels combust in the presence of oxygen, they produce carbon dioxide and water. Therefore, the correct answer to fill in the blank is 'carbon dioxide'.

Combustion of hydrogen and oxygen produces energy and (a)   .

• Carbon dioxide

• Water

• Methane

• Nitrogen

Answer explanation

The combustion of hydrogen and oxygen primarily produces water (H2O) as a byproduct, along with energy. Carbon dioxide, methane, and nitrogen are not products of this reaction.

What is an element?

• A substance made of one type of atom

• A mixture of different atoms

• A compound of two or more elements

• A molecule with multiple atoms.

Answer explanation

An element is defined as a substance made of one type of atom, distinguishing it from mixtures and compounds, which consist of multiple types of atoms or elements.

Explain how the periodic table is organised and its significance in understanding elements.

Answer explanation

The periodic table organizes elements by increasing atomic number and groups them by similar properties. This arrangement helps predict element behavior, understand chemical reactions, and identify trends in elemental characteristics.

An atom contains a nucleus, which contains (a)   and neutrons.

Answer explanation

An atom's nucleus contains protons and neutrons. Therefore, the correct answer to fill in the blank is 'protons', as it specifies the particles present in the nucleus alongside neutrons.

What is the main difference between a compound and a mixture?

• Compounds have a definite amount of each element, while mixtures do not.

• Mixtures have a definite amount of each element, while compounds do not.

• Both have a definite amount of each element.

• Neither have a definite amount of each element.

Answer explanation

The correct choice states that compounds have a definite composition of elements, meaning their ratios are fixed, while mixtures can vary in the amounts of their components, lacking a fixed ratio.