10) Changing States

Substances Can Change from One State to Another

1. Physical Changes: When substances change state, the particles remain the same; only their arrangement or energy changes.

Melting and Freezing

1. Heating Solids: When a solid is heated, its particles gain energy, causing them to vibrate more.

2. At the melting point, particles gain enough energy to break free from their fixed positions. This process is called melting, transforming the solid into a liquid.

3. Freezing occurs when a liquid cools down. As it loses energy, the particles move less, and bonds form between them, turning the liquid back into a solid.

Boiling and Condensing

1. Heating Liquids: When a liquid is heated, its particles gain even more energy, causing them to move faster.

2. At the boiling point, the particles have enough energy to break their bonds and transition from liquid to gas. This process is known as boiling (or evaporating).

3. Condensing happens when a gas cools down. As it loses energy, the particles can no longer overcome the forces of attraction, and bonds form between them, turning the gas back into a liquid.

Energy and State Changes

1. The amount of energy needed for a substance to change state depends on the strength of the forces between its particles.

2. Stronger forces require more energy to break, resulting in higher melting and boiling points.

Predicting the State of a Substance

1. You can predict a substance's state at a specific temperature based on its melting and boiling points:

   • If the temperature is below the melting point, the substance is a solid.

   • If the temperature is above the boiling point, the substance is a gas.

   • If the temperature is between the two points, the substance is a liquid.

Example of State Prediction

1. Consider the following melting and boiling points:

   • Oxygen: Melting point = -219 °C, Boiling point = -183 °C

   • Nitrogen: Melting point = -210 °C, Boiling point = -196 °C

   • Bromine: Melting point = -7 °C, Boiling point = 59 °C

2. At room temperature (25 °C), bromine is a liquid because it melts at -7 °C and boils at 59 °C, while oxygen and nitrogen are gases since their boiling points are below 25 °C.