Introduction
Pressure can be defined as the force exerted perpendicularly per square unit of area of any object. It is represented by the formula,
P = F ⁄ A
where P is the pressure, F is the force exerted on the object, and A is the area of the object. Pressure is measured in pascal, and is classified into absolute, atmospheric, differential, and gauge pressure. A change in pressure has different effects on different states of matter.
Change in Pressure
Since the pressure exerted on an object is the amount of force applied per unit area of that object, a change in area or a change in the amount of exerted force can result in a change in pressure. For example, if the surface area decreases, the pressure increases simultaneously when the surface area decreases, the pressure decreases provided that the force applied remains constant.
Effect of Pressure on the States of Matter
Pressure change can have different effects on different states of matter. By exerting pressure on the matter particles, we can draw them closer. Therefore, applying pressure can cause liquids to turn into solids, and when pressure is applied to a gas that is contained in a cylinder, the gas begins to compress and turn into a liquid. As pressure rises, the volume of the gas reduces, which causes the gas to change into a liquid and then finally a solid. The volume of a gas is inversely related to its pressure and directly relates to the number of molecules it contains.
Pressure has less of an impact on solids because they are non-compressible forms of matter. By applying pressure and lowering the temperature, liquids can be transformed into solids.
Effect of Pressure on Equilibrium
The equilibrium will adjust to minimize a change in the pressure of a gaseous reaction mixture. If the pressure is raised, the equilibrium will change to favour a fall in the pressure. The equilibrium will change if the pressure is reduced to favour an increase.
When a system’s volume is reduced, the pressure will rise (and the temperature is constant). A greater number of collisions occur with the container’s walls. There will be fewer collisions and hence less pressure if there are fewer gas molecules. The equilibrium will change in a way that reduces the number of gas molecules, which will likewise reduce the pressure. To forecast which way equilibrium will shift in response to a change in pressure, we must consider how many gas molecules are involved in the balanced reactions.
For example, the chemical reaction between nitrogen and hydrogen is shown below:
N2 (g) + 3H2 (g)→ 2NH3↑
The proportion in the equation that balances is 1:3:2. In other words, the 1N2 molecule combines with the 3H2 molecule to produce NH3 gas (from the balanced equation). Four molecules of reactant gas must therefore be present to produce two molecules of product gas.
- Pressure buildup will favour the reaction which results in fewer gas molecules. Because there are fewer product gas’ molecules, the forward reaction is more advantageous. Due to the rightward shift in equilibrium, the yield of NH3 will rise.
- The reaction that produces more gas molecules will be more favourable as pressure drops. If there are more reactant gas molecules present, the reverse reaction is more favourable. As a result of the equilibrium shifting to the left, the yield of NH3 will decline.
Some Facts
- Pressure is directly proportional to the temperature.
- In contrast to solids and liquids, gases are more easily subjected to pressure.
- Compared to gases, solids and liquids are less sensitive to pressure.
- When air pressure is raised, the boiling point of water rises.
- The equilibrium will adjust to minimize the change in pressure of the gaseous mixture.
Frequently Asked Questions
1. Does Changing the Size of the Container Affect the Pressure?
Ans: No change in concentration could change the pressure if the equilibrium reaction does not involve a change in the number of molecules in the gas phase. Therefore, altering the container’s size without also altering the pressure would have no impact on the reaction. The number of molecules stays constant and applies the same pressure whether the container size decreases or grows.
2. How can the Physical Condition of the Matter be Altered?
Ans: It is also possible to change the physical state of matter by adjusting the pressure that is applied. For example, by applying pressure and lowering the temperature, gases can liquefy.
3. How does Pressure Affect the Boiling Point of a Liquid?
Ans: All liquids evaporate with an expansion. The expansion and delay of vaporization are the results of pressure on the surface. As a result, when pressure is applied, the boiling point rises.