Question

For each pair, which has higher potential energy? (a) The fuel in your car or the gaseous products in its exhaust (b) Wood in a fire or the ashes after the wood burns

Short answer

The fuel and the wood both have higher potential energy compared to their respective products (exhaust and ashes).

Step-by-step solution

Understand Potential Energy

Potential energy refers to the stored energy in an object or system due to its position, arrangement, or state. It is often released when the state changes.

Analyze Car Fuel and Exhaust

Fuel in a car, such as gasoline, contains chemical potential energy due to the bonds within the fuel molecules. When the fuel burns, it reacts with oxygen to form gaseous products, releasing energy. Thus, the fuel has more potential energy than the exhaust.

Analyze Wood and Ashes

Wood contains chemical potential energy in the form of stored chemical bonds. When wood burns, it reacts with oxygen, releasing energy and producing ashes, which contain less energy. Thus, wood has more potential energy than the ashes produced after burning.

Key concepts

chemical potential energy

Chemical potential energy is the energy stored in the chemical bonds of a substance. This type of energy is what keeps atoms within a molecule together. When a chemical reaction occurs, such as combustion, this stored energy is released.
Let's break it down a bit more:

• A molecule's structure determines how much energy it holds.
• Stronger bonds require more energy to break.
• Once the bonds are broken, energy is released or absorbed, depending on the reaction.

For instance, in the exercise, the fuel in your car has high chemical potential energy because the bonds in gasoline molecules store a significant amount of energy. When these bonds break and new ones form during combustion, energy is released in the form of heat and light.

oxidation reactions

Oxidation reactions are chemical processes where a substance combines with oxygen. This reaction usually releases a lot of energy.
Here are some key points about oxidation reactions:

• Oxidation is a reaction where electrons are transferred from one substance to another.
• In most cases, the substance that loses electrons is oxidized.
• These reactions often involve oxygen, but not always.

In the context of the exercise, burning wood or fuel involves an oxidation reaction where the material (wood or gasoline) reacts with oxygen, leading to the release of stored chemical energy.

energy release in combustion

Combustion is a specific type of chemical reaction where a substance reacts rapidly with oxygen, releasing energy in the form of light and heat. Here’s how it works:

• Combustors (such as wood or gasolina) have high chemical potential energy.
• Upon igniting, these combustors react with oxygen.
• This reaction breaks the bonds in the combustor and forms new bonds in the products (like CO\(_2\) and H\(_2\)O).
• Because products' bonds hold less energy, the excess energy is released as heat and light.

For example, when gasoline burns in your car engine, the stored chemical energy within the gasoline turns into useful mechanical work and energy in the exhaust, which has less stored energy compared to the gasoline itself. Similarly, when wood burns, the chemical energy is released, leaving behind the ashes with much less energy.