This is a part of the What is … Wednesdays feature, where we take scientific topics that might seem convoluted to some and make them more understandable.

Some people have a hard time with algebra, whereas for others it’s a breeze. But when it comes to advanced college coursework in the sciences, a lot more people struggle – though with diligent studying, anyone can be successful, even in difficult classes. One such topic that also probably elicits feelings of fear is thermodynamics.

The laws of thermodynamics 

Simply put, thermodynamics is the study of heat, entropy, work, and how they relate to energy and properties of matter. Thermodynamics is a kind of physics. It is important to various parts of the natural and scientific world, including engines and the weather.

There are four laws that govern the field of thermodynamics.

The zeroth law of thermodynamics defines the concept of thermodynamic equilibrium, which essentially deals with temperature. 

The first law of thermodynamics relates the multiple forms of energy to work and heat transfer. It states that a change in internal energy is equal to the sum of the heat and work done on the system by its surroundings.

Entropy is the subject of the second law of thermodynamics. Entropy can be said to be the amount of states, or randomness, of a system. According to the second law, entropy cannot decrease in a closed system, and will always increase in a spontaneous/non-reversible process.

Finally, the third law of thermodynamics states that as the temperature of a system approaches absolute zero, entropy will become close to a constant value. This is because absolute zero is the coldest temperature, and at that temperature molecular motion stops.

Why should these wordy principles matter to you?

Thermodynamics in daily life

Thermodynamics is relevant to air flow, why hot water boils, and how sunburns form.

Contrary to popular belief, when you put an ice cube in a cup of lemonade, it’s not actually making the lemonade cooler. According to the first law of thermodynamics, heat flows from places of high heat to colder places. 

How, then, do cooling machines like air conditioners and refrigerators work?

They use hot air to their advantage. When pumped into the machines from outside, hot air flows to an evaporator. This evaporator cools a refrigerant, which is a gas that liquifies at low temperatures. As the gas evaporates, it becomes colder. It then flows to a condenser to be turned back into liquid, a process which is exothermic, meaning it releases heat. This heat is pumped out of the machine, which is why the back of refrigerators are warm.

This type of heat transfer is known as convection. All ovens cook by convection, so the term ‘convection oven’ is redundant. Convection involves the movement of heat through a fluid, which in physics is defined as either a liquid or a gas.

There are also two other kinds of heat transfer.

Conduction is heat transfer between objects that are in physical contact with one another. Most metals are particularly good conductors.

And the third method of heat transfer is through radiation. Radiation is different from convection and conduction in that it is the transfer of electromagnetic energy (instead of thermal energy). 

The electromagnetic spectrum contains colors, FM radio waves, and microwaves, among other wavelengths. Humans cannot perceive the entire spectrum. Two parts of the non-visible electromagnetic spectrum are the infrared and ultraviolet regions.

Infrared and ultraviolet rays from the sun are to be blamed for sunburn-not the heat the sun emits. 

Fire is an example of a process that transfers heat through all three mechanisms.

The formal field of thermodynamics originated with an observation made by Swiss physicist Pierre Prevost (1751-1839) in 1761. Prevost noticed that all bodies radiate heat. 

From there, a French physicist named Sadi Carnot (1796-1932) proposed a highly efficient steam engine. Steam engines are based on the second law of thermodynamics. They involve performing work at a high temperature and subsequently releasing energy and heat at a lower temperature.

More recent work dealing with thermodynamics is varied. But one task that can’t be done is reaching absolute zero, or zero degrees Kelvin (0 K). 

It doesn’t stop scientists from trying to, though. In 2003, researchers at the Massachusetts Institute of Technology reached a temperature under 1 nanokelvin, which is one-billionth of one Kelvin. 

At that temperature, atoms move a million times slower than they do at room temperature! This translates into one atom taking 30 seconds to move one inch.

A dynamic experiment

While you might have thought of thermodynamics as a language you couldn’t learn to speak, we’ve laid out the basics for you. For another way to observe thermodynamics at work, try this fun experiment.

Have three cans or bowls, ice cubes, table salt, coarse or rock salt, and a thermometer at hand.

Place equal amounts of ice in each container. Leave one container free of any salt. In the next container, sprinkle one tablespoon of table salt. In the third container, place one tablespoon of coarse or rock salt. 

Check the temperatures of each container after two, five, and ten minutes have passed. Also make note of which trial has the ice that melted first, and that which melts the most.

You will probably find that the ice with the coarse salt melted first, got the coldest, and melted the most. This means that salt lowers the melting point of ice. Download a free observation sheet/worksheet that goes with this experiment by clicking the link below!

ice thermodynamics worksheet

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When ice melts alone, an equal number of water molecules are entering and leaving the solid state. But in the presence of salt, that balance is disrupted. 

Now you might be thinking that oceans don’t freeze because they are saltwater – though you’d only be partially correct. The motion of the ocean is also responsible for its year-round liquid state. 

The salinity of the ocean lowers its melting point to 28.8℉, so still ocean water actually would freeze. However, ocean currents work as a form of convection, transferring heat through the water. Coupled with constant movement, the convection properties of the ocean contribute to the fact that the ocean doesn’t freeze.

By now you should feel very familiar with thermodynamics in your day-to-day activities. Be sure to expand on and share your newfound knowledge!

Delaney​

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