Heat Exchange At Constant Pressure

Key Takeaways

• The first law of thermodynamics is a thermodynamical version of the law of conservation of energy.
• The law states that the total energy in an isolated system remains constant and cannot be created or destroyed, although it can change forms.
• At constant pressure, an isobaric process occurs. The force exerted is constant since the pressure is constant, and the work done is expressed as PΔV.
• Heat should be delivered into the system at a specific rate if gas is to expand at a certain pressure.
• If an ideal gas is kept under isothermal conditions, the product of pressure and volume (PV) is constant.

Table of Contents

• First Law of Thermodynamics
• Constant Pressure and Volume
• Isobaric Expansion (Constant Pressure)
• Heat Exchange at Constant Pressure
• Frequently Asked Questions – FAQs

First Law of Thermodynamics

According to the first law of thermodynamics, the internal energy change of a system equals net heat transfer minus net work done by the system.

The first law of thermodynamics is a thermodynamics-specific version of the law of conservation of energy. It’s commonly stated that the quantity of heat supplied to a closed system minus the amount of work done by the system on its surroundings equals the change in internal energy of the system. The energy of an isolated system is constant, according to the rule of conservation of energy.

If we want to understand how heat is converted into work, we must first understand the conservation of energy principle. The first law of thermodynamics applies the conservation of energy concept to systems in which energy is transferred into and out of the system through heat transfer and work. The first law of thermodynamics, is the equation for, is:

ΔU = Q – W

U is the system’s energy and the change in internal energy is denoted by ΔU, Q is the net heat transferred into the system, and W is the system’s net work.

Read More:

What is Thermodynamics?

Constant Pressure and Volume

Heat transferred to a system can be transformed into internal energy or used to produce work in the environment, according to the first law of thermodynamics. An isobaric process is one in which a gas works on its environment at constant pressure, while an isochoric process is one in which the volume remains constant.

Isobaric Expansion (Constant Pressure)

At constant pressure, an isobaric process occurs. The force exerted is constant since the pressure is constant, and the work done is expressed as PΔV.

Heat should be delivered into the system at a specific pace if gas is to expand at a certain pressure of an isobaric expansion. A moveable piston in a cylinder, for example, ensures that the pressure inside the cylinder is always at atmospheric pressure, although it is separated from the atmosphere. In other words, the system is dynamically connected to a constant-pressure reservoir via a movable barrier.

Heat Exchange at Constant Pressure

At constant pressure, the heat of the reaction equals the system’s enthalpy change (ΔH). Because most chemical reactions occur at constant pressure, enthalpy is employed to calculate the temperatures of the reaction rather than internal energy. Thus, the heat exchanged at constant temperature and pressure is called enthalpy change.

In a thermodynamic system, enthalpy is used to measure energy. The total heat content in a system is equal to the system’s internal energy plus the product of volume and pressure, which equals the quantity of enthalpy.

The developed heat (either absorbed or released) equals the change in enthalpy when a process starts at constant pressure. The total internal energy, denoted by U, and the product of volume and pressure, indicated by PV, is referred to as enthalpy change.

H = U + PV

Read More:

What is Enthalpy?