Effects of Change of Pressure

When we look around us, we notice a wide range of objects in all shapes, sizes, and textures. Everything is made up of a material called matter. From the air, we breathe to the food we eat, and even a single drop of water is all matters. As we glance around, we can see that all of the items stated above take up space and have mass. They have both mass and volume, in other words. Solid, liquid, and gaseous phases of matter are the three basic types of matter. To comprehend the impact of pressure on the three states of matter, we must first comprehend their fundamental qualities.

Liquid state

A liquid is a nearly incompressible fluid that adapts to the shape of its container while retaining a (nearly) constant volume at any pressure. 

If the temperature and pressure are constant, the volume is fixed. When a solid is heated past its melting point and the pressure exceeds the triple point of the substance, it becomes liquid. Despite the existence of intermolecular (or interatomic or interionic) interactions, the molecules have sufficient energy to move about, and the structure is mobile. This means that a liquid’s shape is dictated by its container, not the liquid itself. Water is the most well-known exception, as its volume is often greater than that of the analogous solid. A liquid’s critical temperature is the highest temperature at which it can survive. A transition between solid and gaseous phases is the liquid state of matter. Water exists in three states: ice (solid), liquid (water), and gas (vapour).

Gaseous State

Gas refers to a substance that can be compressed. Not only will gas conform to the shape of the container in which it is contained, but it will also expand to fill it. Intermolecular forces have a modest influence (or none at all in an ideal gas) because the molecules in a gas have ample kinetic energy, and the average distance between neighbouring molecules is much bigger than the molecular dimension. A gas has no definite shape or length, but it fills the whole volume of the container it is kept in. A liquid can be turned into a gas by either heating it to the boiling point under constant pressure or reducing the pressure under constant temperature. 

A vapour is a gas that can be liquefied solely by compression at temperatures below its critical temperature without cooling. When a liquid (or solid) and a vapour are in equilibrium, the gas pressure equals the liquid’s vapour pressure (or solid).

Effect of Pressure on states of Matter

As solids and liquids are non-compressible states of matter, pressure has no effect on them. When pressure is applied to a solid, however, it breaks. On the other hand, applying pressure at a low temperature might cause gases to liquefy. For example, you may have witnessed smoke spreading all around the stage during parties or stage concerts. Dry ice is all there is to it (solid carbon dioxide). Solid carbon dioxide is held at high pressure and instantaneously liquefies when the pressure is dropped to 1 atmosphere.

The space between the particles that make up a substance is what determines its state of matter. As a result, when pressure is given to a gas, it compresses into a liquid, and when pressure is applied to a liquid, it solidifies. Pressure has a negligible influence on solids. When pressure is applied to a substance, the state of the substance changes from:

Gas → Liquid → Solid

Other effect of change of Pressure

The physical condition of matter can also be altered by varying the pressure applied to it. By applying pressure and lowering the temperature, gases can be liquefied. A gas is compressed when high pressure is applied to it, and when the temperature is lowered, it is converted to a liquid. As a result, we can say that gases can be compressed and cooled into liquids.

Examples of Change in Pressure

Under normal temperature and pressure circumstances, carbon dioxide is a gas. By applying pressure at room temperature, it can be liquefied. Under high pressure, solid carbon dioxide (CO₂) is stored. When the pressure is reduced to 1 atmosphere, solid CO₂ is transformed directly to a gaseous state, bypassing the liquid state. This is why solid carbon dioxide is also referred to as dry ice.

Effect of Change of Pressure on Equilibrium

The effect of change of pressure on equilibrium can be understood by Le chatelier’s principle. This is discussed below:

Le Chatelier’s Principle

Le Chatelier’s Principle states that if a system at equilibrium is subjected to the change in conditions such as pressure, temperature or concentration the system will adjust to the counteract the change and restore equilibrium. Therefore, when pressure is altered, the equilibrium position will shift to the minimize the effect of the pressure change.

Gaseous Reactions

The Pressure primarily affects reactions involving the gases because pressure is directly proportional to the concentration of the gases. According to the Le Chatelier’s Principle, if the pressure on the system is increased the equilibrium will shift towards the side with fewer moles of gas to the decrease the pressure and vice versa.

Change in Volume

The Increasing the pressure on a system is akin to the decreasing its volume and vice versa. For reactions involving gases a decrease in the volume will shift the equilibrium towards the side with the fewer moles of the gas and an increase in volume will shift it towards the side with the more moles of gas.

Reaction Quotient and Kp

The reaction quotient (Q) is the ratio of the concentrations of products to the reactants at any given point during the reaction. When pressure changes Q may not be equal to equilibrium constant (Kp) initially. The system will adjust by shifting the equilibrium position until the Q equals Kp again.

Examples:

• Haber Process: In the synthesis of ammonia from the nitrogen and hydrogen increasing pressure favors the formation of the ammonia since there are fewer moles of gas on product side.
• Equilibrium of Dissolved Gases: In the dissolution of gases in liquids increasing pressure increases the solubility of the gases in the liquid phase.

Sample Questions

Question 1: What are the physical and chemical properties of solids?

Answer:

1. Solids are incompressible, which means that the constituent particles are grouped close together and that there is very little space between them.
2. Solids are rigid as there isn’t enough space between the constituent particles, causing it to be hard or fixed.
3. Because of their fixed mass, volume, and shape, solids have a compact arrangement of constituent particles.
4. Molecules have a short intermolecular distance. As a result of this, the force between the constituent particles (atoms, molecules, or ions) is extraordinarily strong.
5. Only the particles that make up the components can fluctuate around their mean location.

Question 2: What is the expansion in physics?

Answer:

Physics is a branch of natural science that studies the nature and properties of matter and energy. Physicists might use either a theoretical or an experimental approach to address their questions.

Expansion occurs when the volume of a solid substance grows without the mass rising. The density of the substance of the drug is reduced as a result. Expansion occurs when the kinetic energy of the solid particles increases as a result of heating.

Question 3: Why do naphthalene balls disappear with time without leaving any solid behind?

Answer:

Naphthalene undergoes sublimation easily i.e., the change of state of naphthalene from solid to gas without the intervention of the liquid state. Thus, naphthalene balls keep on forming naphthalene vapours which disappear into the air with time without leaving any solid.

Question 4: What would be the effect on gas molecules if:

(a) pressure is increased and

(b) pressure is decreased?

Answer:

(a) If pressure is increased, it will produce fewer gas molecules.

(b) If pressure is decreased, it will produce more gas molecules.

Question 5: Why is ammonia stored in storage tanks?

Answer:

The ammonia in storage tank accomplishes two goals. First, it stores ammonia at high pressure to prevent the reverse reaction, which would result in less ammonia and more nitrogen and hydrogen. Second, it conveys a significant message. Methamphetamine, a hazardous substance of abuse, is made from ammonia. Locks and other safety features put inside the tanks assist prevent ammonia theft for use in illegal activities.