Test: Matter - Grade 7 MCQ

In solids, the kinetic energy of molecules primarily allows them to vibrate in place. This limited movement is due to the strong forces of attraction that hold the molecules tightly together.

Solids have the least intermolecular space because their molecules are tightly packed together, resulting in a fixed shape and volume. This close packing is what gives solids their rigid structure. In contrast, liquids have more space, and gases have the most.

The process where a solid changes directly into a gas is called sublimation. An example of sublimation occurs with dry ice (solid carbon dioxide), which transitions to gas without becoming a liquid first.

In solids, molecules vibrate in fixed positions due to strong intermolecular forces that hold them tightly together. Unlike liquids and gases, they do not move freely, which gives solids their definite shape.

Gases do not have a fixed shape or volume. They expand to fill the container they are in, which is a key characteristic that distinguishes gases from solids and liquids.

As a liquid heats up, its molecules gain kinetic energy and begin to move more freely. This increased motion can eventually lead to the liquid boiling and turning into gas if enough heat is applied.

Liquids have a fixed volume but take the shape of their container. This characteristic is due to the molecules being close together yet able to move past one another, allowing liquids to flow.

Latent heat refers to the heat absorbed or released by a substance during a change of state (like melting or boiling) without causing a temperature change. This concept is crucial for understanding phase transitions in matter.

The force of attraction between molecules in solids is very strong due to the close proximity of the molecules. This strong intermolecular force is what gives solids their definite shape and rigid structure, distinguishing them from liquids and gases.

A diatomic molecule is defined as a molecule consisting of two atoms. Common examples include oxygen (O₂) and hydrogen (H₂). This classification is important in understanding the composition of many gases in the atmosphere.

The primary difference is that evaporation occurs only at the surface of a liquid and can happen at various temperatures, while boiling occurs throughout the entire liquid at a specific temperature known as the boiling point.

Matter is defined as anything that has mass and occupies space. This includes all forms of matter—solids, liquids, and gases. Understanding this definition is fundamental in studying physical science, as it encompasses all physical substances around us.

The process of changing from a solid to a liquid is known as melting. This occurs when a solid is heated to its melting point, allowing its molecules to gain sufficient energy to overcome their fixed positions and move freely, thus forming a liquid.

When sweat evaporates, it absorbs heat from the skin, which cools the surface. This cooling effect is beneficial for regulating body temperature, especially in hot conditions.

The space between molecules is referred to as intermolecular space. This space varies between different states of matter, being smallest in solids, larger in liquids, and largest in gases, influencing their properties.

In a gas state, molecules move randomly and are spaced far apart, allowing them to fill any container they occupy. This freedom of movement is a defining characteristic of gases, contrasting significantly with the behavior of molecules in solids and liquids.

The boiling point of a liquid increases with an increase in pressure. This is why pressure cookers can cook food faster; they create a higher pressure environment that raises the boiling point of water.

The melting point of ice at standard atmospheric pressure is 0°C. At this temperature, ice absorbs heat without changing temperature until it fully transitions into liquid water.

The process of a gas turning into a liquid is known as condensation. This occurs when gas molecules lose energy and come together to form a liquid, a process observed when water vapor in the air cools and forms droplets.

The presence of humidity decreases the rate of evaporation. In humid conditions, the air is already saturated with water vapor, which makes it more difficult for additional moisture to evaporate into the air. This is why clothes take longer to dry on humid days.