A system absorbs 196 kJ of heat, and the surroundings do 117 kJ of work on the system. What is the change in internal energy of the system?

The First Law of Thermodynamics is a foundational principle in the study of physics and engineering, particularly within the field of thermodynamics. This law unifies the concepts of heat, work, and internal energy in one elegant statement: the change in the internal energy of a system is equal to the heat added to the system, minus the work the system does on its surroundings.

This law can be mathematically expressed as: \[\Delta U = Q - W\], where \(\Delta U\) represents the change in internal energy, \(Q\) stands for the heat added to the system, and \(W\) is the work done by the system. It is vital to note that work done on the system is considered positive, whereas work done by the system is negative in this context. In teaching this concept, it is crucial to clarify that 'work' in thermodynamics refers to energy transfer resulting from a force acting through a distance, as opposed to the colloquial use of the term.

Thermodynamics is a branch of physics that deals with the relationship between heat and other forms of energy. In essence, it studies the effects of changes in temperature, pressure, and volume of physical systems at the macroscopic scale. The principles of thermodynamics are widely applied in various scientific and engineering disciplines, including mechanical engineering, chemical engineering, and environmental science.

There are four main laws of thermodynamics that describe how energy moves within these systems, how it changes form, and how it can create work. Thermodynamics plays a crucial role in understanding the physical world and technology, such as engines, refrigerators, and even biological processes. As educators, emphasizing real-world applications can aid students in appreciating the relevance of thermodynamic principles.

Heat, in thermodynamics, is a form of energy transfer between systems or a system and its surroundings, driven by a temperature difference. When a system receives heat, its internal energy increases unless the system does work or there is a change in its state, such as phase transition.

Understanding Heat Transfer

Heat can be transferred in three ways: conduction, convection, and radiation. Conduction occurs through direct contact, convection through fluid movement, and radiation through electromagnetic waves.

It is essential for students to grasp that when they encounter problems involving heat transfer, they must consider the direction of energy flow. Heat absorbed by a system is regarded as positive, and heat released by a system is negative, which directly influences the calculation of a system's change in internal energy.

In the realm of thermodynamics, 'work' is a term that represents the energy transfer that occurs when a force is applied to an object causing a displacement. Work can be done by a system or on a system, and this distinction is pivotal in calculating energy changes.

Work in Thermodynamic Processes

For example, the compression of a gas within a piston involves work done on the gas, resulting in an increase in its internal energy. Conversely, when the gas expands, it does work on the surroundings, which typically leads to a decrease in the gas's internal energy.

In our original exercise, the work is being done on the system, which adds energy to it. Therefore, students should remember the sign convention: work done on the system is positive, contributing to an increase in the internal energy. Clarifying the difference between these conventions is essential in helping students solve thermodynamic problems accurately.