Liquid State

Shape Image One
  • No Comments
  • Admin
  • May 1, 2023
9th Chemistry Ch#05 Physical States of Matter Liquid State

Liquid State

advanced divider

In chemistry, the liquid state refers to one of the four fundamental states of matter (the others being solid, gas, and plasma), in which a substance has a definite volume but not a definite shape.

Properties of Liquid:

Liquids are one of the three states of matter, the others being solids and gases. Here are some properties of liquids that are important to know:

  1. Liquids have a definite volume but no definite shape: Unlike solids, liquids do not have a fixed shape and take the shape of the container they are placed in. However, they do have a definite volume and cannot be compressed easily.

  2. Liquids are fluid: Liquids flow and can be poured from one container to another. They also exhibit viscosity, or the resistance to flow. Viscosity varies among liquids and is affected by factors such as temperature and pressure.

  3. Liquids have a lower density than solids: Liquids are generally less dense than solids and tend to expand when heated. They also have a higher density than gases.
  4. Liquids can evaporate: Liquids can change into a gas through the process of evaporation, which occurs when molecules at the surface of the liquid gain enough energy to overcome the forces holding them in the liquid phase.
  5. Liquids can be separated by physical means: Liquids can be separated from mixtures using physical methods such as filtration, distillation, and chromatography.
  6. Liquids have a high surface tension: Liquids tend to form a surface or interface with the air, and this surface tension can be observed when droplets form on a surface or when insects can walk on water.
  7. Liquids can conduct electricity: Some liquids, such as saltwater or acids, can conduct electricity due to the presence of ions. However, most liquids are poor conductors of electricity.

Evaporation:

Evaporation is the process by which a liquid changes into a gas or vapour state.

Explanation:

This occurs when the molecules of a liquid gain enough energy to break their bonds with each other and escape into the surrounding atmosphere as a gas.

During evaporation, the liquid absorbs energy from its surroundings, usually in the form of heat, which increases the kinetic energy of the liquid molecules and causes them to move faster. As they move faster, they collide with each other and with the surface of the liquid, and some of them escape into the air as a gas or vapour.

Evaporation plays an important role in many natural and industrial processes, including the water cycle, where it helps to transfer water from the surface of the earth to the atmosphere, and in cooling systems, where it is used to remove heat from liquids or other materials.

Factors Affecting Evaporation:

Evaporation is the process by which a liquid substance changes into its gaseous state due to the supply of heat energy. Several factors can affect the rate of evaporation, including:
  1. Temperature: An increase in temperature causes an increase in the kinetic energy of the molecules in the liquid, resulting in more molecules escaping into the atmosphere and, therefore, an increase in the rate of evaporation.
  2. Humidity: The amount of moisture already present in the air affects the rate of evaporation. As the humidity of the air increases, the rate of evaporation decreases because there is less room for more moisture in the air.
  3. Surface Area: A larger surface area of the liquid exposed to the atmosphere results in a faster rate of evaporation.
  4. Pressure: The rate of evaporation is also affected by the pressure of the atmosphere. At high altitudes, where the atmospheric pressure is lower, the rate of evaporation is faster compared to at sea level.

Vapour pressure:

Vapour pressure is the pressure exerted by the vapour of a substance when it is in equilibrium with its liquid or solid state. In simpler terms, it is the pressure that is created by the molecules of a substance when they evaporate from a liquid or solid surface and enter the gas phase.

Explanation:

When a substance is heated, its molecules gain energy and start to move faster. Some of these molecules may have enough energy to overcome the attractive forces between them and escape from the surface of the liquid or solid to become a gas. This gas then exerts a pressure on the surrounding environment.

The vapour pressure of a substance depends on the temperature and the strength of the intermolecular forces between the molecules of the substance. Generally, substances with weaker intermolecular forces have higher vapour pressures because their molecules are more likely to escape into the gas phase.

Vapour pressure is an important concept in chemistry and physics, and it is used to explain phenomena such as boiling and evaporation.

Factors Affecting Vapour Pressure:

Vapour pressure is the pressure exerted by a vapour in equilibrium with its condensed phase at a certain temperature. The following factors can affect vapour pressure:

  1. Temperature: Vapour pressure increases with increasing temperature. This is because at higher temperatures, more molecules have enough kinetic energy to escape from the condensed phase and enter the vapour phase

  2. Intermolecular forces: Vapour pressure decreases with increasing intermolecular forces. This is because stronger intermolecular forces hold the molecules in the condensed phase more tightly, making it harder for them to escape and enter the vapour phase.

  3. Surface Area: Vapour pressure increases with increasing surface area. This is because more molecules are exposed to the air and can escape into the vapour phase.

Boiling Point:

The boiling point of a liquid is the temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure acting on the liquid. At this temperature, the liquid will boil and evaporate into a gas.

Explanation:

The boiling point of a liquid depends on a variety of factors, including the pressure, the chemical composition of the liquid, and the presence of other substances in the liquid.

For example, at standard atmospheric pressure (1 atm), water boils at 100 degrees Celsius (212 degrees Fahrenheit). However, at higher altitudes where the atmospheric pressure is lower, the boiling point of water will be lower as well. Conversely, increasing the pressure on a liquid will increase its boiling point.

The boiling point of different liquids can vary widely. For example, the boiling point of ethanol (a common alcohol) is 78.5 degrees Celsius (173.3 degrees Fahrenheit), while the boiling point of mercury (a heavy metal) is 357 degrees Celsius (674.6 degrees Fahrenheit).

Freezing Point:

The freezing point of a liquid is the temperature at which it changes from a liquid state to a solid state. This temperature varies depending on the substance.

Example:

the freezing point of water is 0°C (32°F) at standard atmospheric pressure. However, the freezing point of other liquids, such as alcohol or gasoline, is much lower than that of water.

It’s worth noting that adding certain substances to a liquid can also change its freezing point. For example, adding salt to water can lower its freezing point, which is why salt is often used to de-ice roads during the winter.

Diffusion:

Diffusion is the process by which particles or molecules move from an area of higher concentration to an area of lower concentration. This movement occurs due to the random motion of particles and does not require any external energy input.Here are some examples of diffusion in everyday life:

  1. Perfume: When you spray perfume, the scent particles diffuse through the air and spread throughout the room.

  2. Tea: When you steep a tea bag in hot water, the tea particles diffuse out of the bag and into the water, creating a uniform flavour

Factors Affecting Diffusion

Diffusion is the process by which particles move from an area of high concentration to an area of low concentration. The factors that affect diffusion include:

  1. Temperature: An increase in temperature increases the kinetic energy of particles, causing them to move faster and diffuse more quickly.
  2. Concentration gradient: The larger the difference in concentration between two areas, the faster diffusion will occur.

  3. Surface area: The larger the surface area available for diffusion, the faster diffusion will occur.

  4. Molecular weight: Smaller molecules diffuse more quickly than larger molecules.

    Mobility:

    Mobility in liquids refers to the ability of a substance to move or flow freely within a liquid. The mobility of a substance in a liquid is determined by its size, shape, and chemical properties, as well as the viscosity and density of the liquid.

    Factors Affecting Mobility:

    The factors that affect mobility (or how easily particles can move) in a liquids  are:

    1. Viscosity: Viscosity is the resistance to flow in a liquid. Liquids with high viscosity, such as honey, flow slowly and have low mobility, while liquids with low viscosity, such as water, flow easily and have high mobility.
    2. Temperature: Temperature affects the mobility of particles in a liquid. As temperature increases, particles in the liquid gain energy and move faster, resulting in increased mobility. As temperature decreases, particles in the liquid move slower and mobility decreases.

    3. Pressure: Pressure can also affect the mobility of particles in a liquid. As pressure increases, particles are compressed closer together, resulting in decreased mobility. As pressure decreases, particles have more space to move and mobility increases

      Density:

      In science, density is defined as the mass of a substance per unit volume. The formula for calculating density is:

      Density =Mass / Volume

      Here are some examples of typical densities for common substances:

      • Water: 1 g/mL
      • Aluminium: 2.7 g/cm³
      • Iron: 7.9 g/cm³
      • Copper: 8.9 g/cm³
      • Gold: 19.3 g/cm³

      It’s important to note that density can vary depending on temperature and pressure, so these values are approximate and may change under different conditions.

      Factors Affects Density:

      Density is a physical property of a substance that refers to the amount of mass per unit volume. The following factors can affect the density of a substance:
      1. Temperature: As temperature increases, the density of a substance generally decreases. This is because the molecules of the substance become more energetic and spread out, taking up more space and reducing the overall density. 
      2. Pressure: Increasing the pressure on a substance can cause its density to increase. This is because the molecules of the substance are forced closer together, reducing the amount of space they occupy and increasing the overall density
      Previous Topic
      Back to Lesson
      Next Topic