Answer key

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Last edited 25 days ago by Learn LoopHQ.

Chapter: 02. Matter

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Sublimation is a unique process where certain substances directly change from a solid to a gaseous state upon heating, completely bypassing the liquid phase. A common example of a sublimable substance is dry ice, which is solid carbon dioxide. Conversely, deposition is the process where a vapor or gas directly transforms into a solid state upon cooling, again without passing through a liquid phase. An example of deposition is the formation of frost on cold surfaces when water vapor in the air directly freezes into ice crystals.

A chemical change is a transformation where a new substance is formed, and this new substance possesses properties entirely different from the original material. Heating can trigger such a change by providing the necessary energy for chemical reactions to occur, rearranging atoms into new molecular structures. For example, when paper is burned, heating causes its cellulose to react with oxygen, forming ash, carbon dioxide, and water vapor. The ash and gases are entirely new substances with properties distinctly different from the original paper, confirming it as a chemical change.

All three states of matter generally expand when heated because heating increases the kinetic energy of their constituent molecules. This increased energy causes the molecules to move more vigorously and vibrate more intensely. As they move more, the average distance between molecules, or intermolecular space, increases. This greater separation of molecules leads to an overall increase in the volume occupied by the substance, resulting in its expansion.

In the solid state, molecules are very closely packed with negligible intermolecular space and very strong intermolecular forces, allowing them only to vibrate about fixed positions. Liquids have loosely packed molecules with more intermolecular space and weaker intermolecular forces than solids, enabling their molecules to move freely within the liquid’s boundaries. Gases feature molecules that are far apart with very large intermolecular spaces and negligible intermolecular forces, allowing their molecules to move absolutely freely in any direction without a definite arrangement.

Matter is anything that has mass and occupies space. Its first fundamental property is having mass, which is the amount of matter contained in an object, as demonstrated when a glass with water or stones weighs down a balance. The second property is occupying space, meaning matter takes up a certain volume, which is evident when a stone placed in a full glass of water causes the water to overflow. These two characteristics are universal to all forms of matter.

Interconversion of states of matter refers to the physical process where a substance changes from one state (solid, liquid, or gas) to another and can return to its original state without altering its chemical composition. This process is primarily driven by changes in temperature or pressure. During melting, heating a solid increases the kinetic energy of its particles, causing them to vibrate vigorously enough to overcome intermolecular forces and transition to a liquid. Similarly, during boiling, continued heating of a liquid further increases particle kinetic energy, allowing molecules to escape as a gas.

The four main characteristics of matter particles are that they are very small in size, always in continuous random motion (due to kinetic energy, known as Brownian motion), held together by intermolecular forces of attraction, and possess spaces between them called intermolecular spaces. The relationship between intermolecular force and space is inverse: when the intermolecular force of attraction is maximum, the intermolecular space is minimum. Conversely, as the intermolecular force of attraction decreases, the intermolecular space increases.

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