Provide an example of internal energy and enthalpy.

Internal energy is the sum of all the kinetic and potential energies of the particles that make up a system. Enthalpy, on the other hand, is the sum of the internal energy and the product of pressure and volume of a system.

An example of internal energy can be seen in a gas-filled balloon. The gas molecules inside the balloon are in constant motion, colliding with each other and the walls of the balloon. This motion creates kinetic energy, which contributes to the internal energy of the system. The potential energy of the gas molecules is also a part of the internal energy, as it represents the energy stored in the bonds between the atoms.

Enthalpy can be observed in a chemical reaction, such as the combustion of methane. The reactants, methane and oxygen, have a certain internal energy before the reaction takes place. During the reaction, the bonds between the atoms are broken and new bonds are formed, resulting in a change in internal energy. The pressure and volume of the system may also change during the reaction, contributing to the enthalpy of the system.

Understanding internal energy and enthalpy is important in thermodynamics, as it allows us to predict and analyse the behaviour of systems under different conditions. It also has practical applications in fields such as engineering and chemistry.