Lesson: Chapter - 9


The Chemistry exam will test your ability to understand the concepts of enthalpy, entropy, and free energy for various systems. All of these concepts fall under the broad category of chemical thermodynamics, and thermodynamics is the area of chemistry that deals with energy relationships. You will also be expected to find values for these energy relationships and use specific heat and energy changes in different systems. We will begin this chapter by introducing some terms and concepts that are probably already familiar to you.

The law of conservation of energy (also known as the first law of thermodynamics) states that in the course of a chemical reaction, energy can neither be created nor destroyed. But what exactly is energy? So far we’ve talked about it only tangentially, but here we can define energy (E) as the ability to do work or produce heat. Energy is measured in joules.

Heat (q) refers to the transfer of energy in a physical or chemical process: heat always flows from a warmer object to a cooler one. Heat is also measured in joules. The sum of all of the potential and kinetic energy in a system is known as the internal energy of the system.

Energy comes in several different forms. Let’s go through a few of them now. Potential energy, in chemical terms, is the energy stored in chemical bonds. Energy is needed in order to break bonds and is given off when bonds form. Another type of energy, called kinetic energy, exists in matter in motion. Usually the energy of particles is proportional to the temperature, in kelvins, of the system as well as the mass and the velocity of the object: KE = 1/2 mv2.

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