Introductory Chemical Engineering Thermodynamics

Chapter 2. The Energy Balance

When you can measure what you are speaking about, and express it in numbers, you know something about it. When you cannot measure it, your knowledge is meager and unsatisfactory.

Lord Kelvin

The energy balance is based on the postulate of conservation of energy in the universe. This postulate is known as the first law of thermodynamics. It is a “law” in the same sense as Newton’s laws. It is not refuted by experimental observations within a broadly defined range of conditions, but there is no mathematical proof of its validity. Derived from experimental observation, it quantitatively accounts for energy transformations (heat, work, kinetic, potential). We take the first law as a starting point, a postulate at the ...