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What the Earth’s core and rust have in common... let's talk energy dynamics

The heat given off by the Earth's molten core, and the gradual rusting of steel are all natural processes which can be slowed down, or speeded up depending on a variety of influencing factors, such as the chemical conditions of the environment.

Such processes are governed by the laws of thermodynamics, which is the science of how energy transforms through chemical reactions. This area of study began when we had to figure out how much energy we needed to generate from certain amounts of coal in the 1800s, with scientists such as Josiah Willard Gibbs (1839 – 1903) and Lord Kelvin (1824 -1907). Marie Curie (1867 – 1934) then made an advancement by discovering nuclear reactions in the early 1900s, with her pioneering work in radioactivity, eventually leading to her death in 1934 through her exposure to radioactivity in her research and hospital work.

While chemical reactions were first studied through the 1800s, mainly to optimize for the energy requirements of the industrial revolution, nuclear reactions were then studied in the early 1900s, which could then explain certain natural processes. For example, the reason that the center of the Earth is still generating heat at its molten core. Lord Kelvin was a chemist and physicist, who tried to deduce the age of the Earth from the geothermal gradient.

He struggled with the mystery of why the center of the Earth was hot, as non-nuclear science would suggest the core of our planet should have cooled down a long time ago. Though, with the discovery of nuclear reactions, by Marie Curie, this mystery was resolved, since nuclear reactions generate heat actively in the Earth’s core, rather than a hot core, gradually cooling down.

Thermodynamics can tell you where a reaction will end up, in this case, we know that the Earth’s core will eventually cool down. The question, though, is how long will that take?

Predicting patterns such as these, whether they are nuclear or chemical reactions, is a scientific challenge. When travelling, various factors describing how you get there; your route, how you start and finish and how fast you travel, which is analogous to the factors influencing different systems in nature, which make their way to their destination (end-state).

Imagine a piece of steel on a bridge across a river. It will eventually corrode, and rust, becoming part of the sediment of the river. The question is how long that would take. How can we slow the process down? What determines the speed at which the reaction occurs? In this case it is the oxidation to iron oxide in the steel. How fast it occurs depends on the surrounding conditions – such as the presence of water and the air.

Can we predict how fast the steel will corrode? The answer is, we can try, though, not very well.

The rate of the corrosion reaction has been modelled through various scientific methods, though it remains a challenge. This is because we do not really understand the mechanics. We know oxygen will react with iron in the bridge, though do not understand how fast they produce the reaction products (iron oxide in this case). The rate can be measured in the lab, where corrosion might typically occur at 0.1mm per year for a piece of steel.

This reaction requires water as a solvent, and oxygen which reacts with the metal. So, if you can keep the surface dry, you will not have corrosion under normal circumstances, and painting the surface can protect the material from exposure to water and oxygen. This in turn, will help us slow down the natural process.

It has always been a challenge to understand how processes flow in nature, and come to their end-state; whether it be the generation of heat at the Earth’s molten core, the corrosion of steel, or even a holiday trip to our destination. However, advancements in science have assisted us with this over three centuries, having become key to our technological developments whether it be the engineering, medical or information technology industries.