A foundational cornerstone of chemical engineering is the mass and energy balance. This principle states with absolute certainty that mass and energy are conserved. In a steady-state, continuous process, the mass and energy entering a system must precisely equal those exiting – not approximately, but exactly. If there’s a discrepancy in these numbers, it indicates a missing element, like material lost through a leak or an uncalibrated thermocouple or flowmeter. Our unwavering trust in the mass and energy balance informs us of such anomalies.

The first significant challenge to the conservation of energy ended with stronger trust in this conservation law

When the thermodynamics pioneers discovered (or created) the concept of energy and its conservation, time was still required for the above “trust” component to become what it is today. Indeed, in 1925 the conservation of energy was questioned at the highest levels of science when physicists couldn’t close the energy balance of beta-decay in which a neutron decays into a proton plus an electron. What they didn’t (or couldn’t) realize then was that the reaction releases another product, the yet-to-be-discovered neutrino, later to be called an anti-neutrino. Embracing the conservation of energy, Wolfgang Pauli hypothesized the existence of this particle for it was the only way that energy could be conserved. His absolute trust in this conservation law led to the neutrino’s eventual discovery. The details behind this discovery process make for an educational read as I share in Chapter 23 of my book Block by Block – The Historical and Theoretical Foundations of Thermodynamics. Thank you for listening!

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