Thermodynamics and Internal Energy Change

Thermodynamics is the study of the interaction between heat, work, temperature, and energy. In its broadest sense, thermodynamics is concerned with the movement of energy from one place to another and from one form to another.The essential concept is that heat is a sort of energy that correlates to a specified quantity of mechanical labour.

Thermodynamic states 

The application of thermodynamic principles begins with the definition of a system that is distinct in some way from its surroundings. The system may be a sample of gas within a cylinder with a moving piston, a steam engine, a marathon runner, the planet Earth, a neutron star, a black hole, or perhaps the entire universe.Systems can freely exchange heat, work, and other forms of energy with their surroundings in general.

The current state of a system is referred to as its thermodynamic state.The state of a system is determined by the temperature, pressure, and volume of a gas in a cylinder with a moving piston.These attributes are defining parameters that have defined values at each state and are unaffected by how the system arrived at that state. In other words, any change in the value of a property is determined solely by the system’s initial and final states, not by the path taken by the system from one state to the next. These characteristics are found in state functions, which are a form of property .On the other hand, the work done as the piston advances and the gas expands, as well as the heat the gas absorbs from its surroundings, are all dependent on how precisely the gas expands.

Internal Energy Change

Internal energy is the amount of energy contained within a thermodynamic system. It’s the quantity of energy needed to construct or prepare a system in any given internal state. It does not include the kinetic energy of the system’s overall motion, as well as the potential energy of the system as a whole due to external force fields, which includes the energy of the system’s surroundings’ displacement.It keeps track of the system’s energy gains and losses as a result of changes in its internal condition.  The difference between a reference zero set by a standard state and the internal energy is measured.The thermodynamic processes that transport the system between the reference state and the current state of interest determine the difference.

Internal energy is a wide concept that is difficult to quantify.Transfers of chemical compounds or energy as heat, as well as thermodynamic work, are thermodynamic processes that characterise internal energy .These processes are measured by changes in the system’s many variables, such as entropy, volume, and chemical composition.Considering all of the system’s inherent energies, such as the static rest mass energy of its constituent materials, isn’t always necessary. The first law of thermodynamics describes the change in internal energy as the difference between the energy provided to the system as heat and the thermodynamic work done by the system on its surroundings when mass transfer is restricted by impermeable enclosing walls. The system is said to be isolated if neither substance nor energy passes through the confining walls, and its internal energy cannot alter.

Mathematically, we define the change in internal energy ΔU by the first law of thermodynamics:

 ΔU = Q− W

Q= Heat

W=Work done

Mass:

Mass is a conserved property, similar to energy, in that it cannot be created or destroyed. Einstein’s formula E = mc2, where c is the speed of light, can be used to convert mass and energy to each other. Except for nuclear reactions, all processes follow the conservation of mass concept.

According to the law of conservation of mass, the mass of the reactants must equal the mass of the products in a low-energy thermodynamic process.

Molecular mass:

Molar mass (M) is the mass of one mole of a given element or compound; as a result, molar masses are often referred to as molecular weights and are expressed in grammes per mole (g mol–1).

The total atomic mass of all atoms in a molecule, calculated using a scale with atomic weights of 1, 12, 14, and 16 for hydrogen, carbon, nitrogen, and oxygen, respectively.

The rate at which molecules in a gas move is related to temperature and inversely proportional to the molar mass of the gas. To put it another way, as a gas sample’s temperature rises, the molecules accelerate, raising the root mean square molecular speed.

To a degree, a high molecular weight promotes chemical resistance. It takes more damage to the molecules’ major chains before the material’s strength is compromised. The viscosity of a material with a high molecular weight increases, making it more difficult to process using traditional methods.

Heat capacity

Heat capacity is defined as the ratio of heat absorbed by a substance to the temperature change.

The amount of material being considered, which is usually a mole, is usually expressed as calories per degree (the molecular weight in grams).Specific heat is the heat capacity in calories per gramme.

At sufficiently high temperatures, the heat capacity per atom for all elements tends to be the same. At room temperature, this approximation is already good for metals with higher atomic weights.

Heat capacity and temperature variation in other materials are determined by atomic energy levels (available quantum states). Heat capacities are measured with various calorimeters, and heat-capacity measurements became essential as a technique of estimating the entropies of various materials after the establishment of the third law of thermodynamics.

Conclusion:

According to the rule of energy conservation, the change in internal energy is equal to the heat transferred to, less the work done by, the system. If the sole work done is a change in volume at constant pressure, the enthalpy change is precisely equal to the heat transmitted to the system