In biological systems like human metabolism, the first law of thermodynamics is manifested in the energy balance between the energy intake, in the form of food, and energy expenditure through basal metabolic rate, physical activity, and thermogenesis. Energy is neither created nor destroyed but converted from chemical energy in food to other forms like kinetic energy, potential energy, and thermal energy. The law helps in understanding and quantifying these energy transformations, providing a foundation for studies related to diet, exercise, and overall energy balance in biological organisms, emphasising the universality of this law across physical and biological realms.

The first law of thermodynamics is considered a statement of energy conservation because it asserts that energy cannot be created or destroyed, only transformed from one form to another. This law encapsulates the perpetual constancy of total energy in a closed system, underscoring the transformation between internal energy, heat, and work. Distinguishing it from the conservation of mass principle, while the latter posits the constancy of mass in closed systems, the first law of thermodynamics focuses explicitly on energy transactions and transformations, serving as a cornerstone for understanding complex energetic interactions in physical systems.

Yes, the first law of thermodynamics can be extended to open systems by incorporating terms that account for the energy associated with mass entering or leaving the system. In such cases, the law adapts to include not just the energy transferred as heat and work, but also the energy carried by the mass that is added or removed. This energy includes the internal, kinetic, and potential energies of the incoming or outgoing mass. Engineers and scientists often use this extended version of the first law to analyse systems like rockets and jets, where both mass and energy are exchanged with the surroundings.

External factors such as atmospheric pressure directly impact the work done by or on a system. For instance, in the context of a gas enclosed in a piston, the atmospheric pressure exerts a force on the piston. The work done in expanding or compressing the gas is not only dependent on the internal pressure of the gas but also on the external atmospheric pressure. In calculations involving work done, especially in isobaric processes, the net pressure (the difference between internal and external pressures) is considered to accurately evaluate the work associated with the volume change, crucial for applying the first law of thermodynamics effectively.

The type of gas particles affects the change in internal energy through the degrees of freedom of the particles, which in turn influences the specific heat capacity. Monatomic gases have 3 degrees of freedom, diatomic have 5, and polyatomic have 6 or more, depending on their structure. The more degrees of freedom, the more ways the gas can store internal energy. Consequently, for a given amount of heat added, diatomic and polyatomic gases would have a smaller rise in temperature compared to monatomic gases, due to their higher heat capacity. This understanding is integral to applying the first law of thermodynamics in diverse scenarios involving different types of gases.