Question

If there is no change in pressure at any point of the system with time, then the system is said to be in:
1. chemical equilibrium
2. thermal equilibrium
3. phase equilibrium
4. mechanical equilibrium

Answer 1

Correct Answer - Option 4 : mechanical equilibrium

Explanation:

State and Equilibrium:

• At a given state, all the properties of a system have fixed values. As a result, if the value of even one property changes, the state will change.
• In an equilibrium state, there are no unbalanced potentials (or driving forces) within the system. When a system is isolated from its surroundings, it does not change.

A system can attain any or all of the following equilibrium:​

1. Mechanical equilibrium:

• ​​When there is no change in pressure at any point of the system. However, due to gravitational effects, the pressure within the system may vary.
• Additionally, in terms of momentum, a system is in equilibrium if all of its parts have the same momentum and if the system's velocity remains constant, the system is also in equilibrium. 

2. Chemical equilibrium: 

• When the chemical composition of a system does not change with time, i.e., no chemical reactions occur.
• Chemical equilibrium occurs when both reactants and products are present in concentrations that have no further tendency to change with time, resulting in no noticeable change in the system's properties.

3. Thermal equilibrium:

• ​​The temperature is the same throughout the entire system.
• When two physical systems are connected by a heat-permeable path, they are in thermal equilibrium if there is no net flow of thermal energy between them.
• The zeroth law of thermodynamics governs thermal equilibrium.

4. Phase equilibrium:

• Phase equilibrium is the study of the equilibrium which exists between or within different states of matter namely solid, liquid and gas.​
• A phase is a region in which intermolecular interactions are spatially uniform, or in other words, the system's physical and chemical properties are consistent throughout the region. A component, such as allotropes of an element, can exist in two different phases within the same state.