Under the hood: The chemistry of cars - Cynthia Chubbuck

Summary

The process of starting a car's engine involves complex chemistry, where gasoline and air mix, ignite, and create gases that power the piston. To prevent engine damage from excess heat, the cooling system circulates a special liquid. While water might seem like a logical choice, it has a low freezing and boiling point, making it unsuitable. Instead, a solution of ethylene glycol and water is used, offering a lower freezing point and higher boiling point. This solution keeps the engine cool, absorbs heat, and returns safely to the engine. The key is to balance the solution for optimal protection.

Takeaways

• 😀 Over one billion cars are in use worldwide today, and they provide not only transportation but also a chemistry lesson.
• 😀 The process of starting a car involves the mixing of gasoline and air, which is ignited to form gases that push the piston in the engine.
• 😀 Combustion in car engines is an exothermic reaction, releasing a lot of heat, some of which is absorbed by the engine components.
• 😀 The cooling system in cars absorbs, transports, and dissipates heat to prevent engine damage, using a liquid to regulate temperature.
• 😀 Water might seem like an ideal cooling solution due to its high specific heat, but its freezing point and boiling point cause potential problems.
• 😀 Using water alone in the cooling system can cause issues like frozen radiators in cold weather and overheating due to water's relatively low boiling point.
• 😀 A solution of ethylene glycol and water is commonly used instead of pure water in car cooling systems due to its adjusted freezing and boiling points.
• 😀 Solutions have colligative properties like freezing point depression and boiling point elevation, which help prevent freezing and excessive boiling in car engines.
• 😀 The freezing point of an ethylene glycol and water solution can go as low as -55°C, and the boiling point can rise to 113°C, providing optimal protection.
• 😀 At higher concentrations of ethylene glycol, the freezing point starts to rise, demonstrating that there can be too much of a good thing in the cooling solution.
• 😀 The cooling system ensures effective engine cooling by circulating the mixture through the engine and radiator, where it is cooled by air before returning to the engine.

Q & A

What happens when a car's engine starts?

When a car's engine starts, gasoline is injected into the engine cylinders, mixing with air. This mixture is then ignited by a spark, causing combustion. The reaction produces gases that expand and push the piston, which powers the engine.

Why is heat released during combustion in a car engine?

Combustion is an exothermic reaction, meaning it releases heat. This heat is generated when the fuel burns and expands, pushing the piston. Some of this heat escapes through the tailpipe, but much of it stays in the engine block.

How does the car's cooling system work?

The car's cooling system circulates a liquid throughout the engine to absorb and transport the excess heat. This prevents the engine's metal components from deforming or melting due to the high temperatures generated during combustion.

Why is water not used as a coolant in car engines?

While water has a high specific heat, it is not used because of its freezing and boiling points. Water freezes at 0°C and expands, which can crack the radiator. It also boils at 100°C, which is too low for the high temperatures in car engines.

What is a solution, and how is it used in car engine cooling?

A solution is a homogeneous mixture of a solute and a solvent. In car engines, a solution of ethylene glycol and water is used as the coolant. This solution has a lower freezing point and higher boiling point than pure water, making it more suitable for extreme temperatures.

What are colligative properties, and how do they affect car engine coolants?

Colligative properties are properties of solutions that depend on the number of solute particles present. In the case of car coolants, these properties include freezing point depression and boiling point elevation, meaning the more solute added (like ethylene glycol), the lower the freezing point and higher the boiling point of the coolant.

How does the presence of solute affect freezing and boiling points?

The presence of solute particles in a solution prevents the molecules from forming a crystal structure when freezing, lowering the freezing point. Similarly, the solute lowers the vapor pressure of the solution, requiring a higher temperature for boiling to occur.

How does the radiator help cool the engine?

The radiator cools the heated coolant by using a fan and the flow of air through the front of the car. As the coolant passes through the radiator, it loses heat and is then circulated back to the engine.

What is the effect of increasing the amount of ethylene glycol in the coolant solution?

Increasing the amount of ethylene glycol in the coolant solution lowers the freezing point further and raises the boiling point. However, beyond a certain point, too much ethylene glycol can cause the freezing point to rise, making the coolant less effective.

What are the ideal properties for a car engine coolant?

The ideal car engine coolant should have a high specific heat, a low freezing point, and a high boiling point. These properties allow the coolant to absorb heat efficiently, remain in liquid form at extreme temperatures, and protect the engine from overheating or freezing.