Question

Label each of the following as either a physical process or a chemical process: (a) rusting of a metal can, (b) boiling a cup of water, (c) pulverizing an aspirin, (d) digesting a candy bar, (e) exploding of nitroglyerin.

Short answer

The processes are classified as follows: (a) rusting of a metal can - chemical process, (b) boiling a cup of water - physical process, (c) pulverizing an aspirin - physical process, (d) digesting a candy bar - chemical process, and (e) exploding of nitroglycerin - chemical process.

Step-by-step solution

Process (a): Rusting of a metal can

Rusting is a chemical process because it involves the interaction of oxygen with the metal, resulting in the formation of rust (a new substance with different properties). In the case of a metal can, the rusting process involves the conversion of iron into iron oxide.

Process (b): Boiling a cup of water

Boiling a cup of water is a physical process because the water molecules are converting from the liquid state to the gaseous state (steam) at the boiling point, but there is no change in the chemical composition of water.

Process (c): Pulverizing an aspirin

Pulverizing an aspirin is a physical process because it involves the breaking or grinding of aspirin into smaller particles without any change in its chemical composition. The physical state of aspirin changes (from solid to powder), but its chemical properties remain the same.

Process (d): Digesting a candy bar

Digesting a candy bar is a chemical process because the candy bar undergoes a series of chemical reactions in the body to break down its components, such as sugars, proteins, and fats, into simpler substances that can be absorbed and used by the body for energy and other functions.

Process (e): Exploding of nitroglycerin

The exploding of nitroglycerin is a chemical process because it involves a rapid chemical reaction in which nitroglycerin decomposes into simpler substances, releasing a large amount of energy as heat and pressure. This reaction results in the formation of new substances, such as nitrogen, carbon dioxide, and water.

Key concepts

Rusting of Metals

When metal objects are exposed to oxygen and moisture, they undergo a process known as rusting. This is not just a surface alteration; it is a chemical process that changes the very composition of the metal. Iron, for example, reacts with oxygen to form iron oxide, commonly called rust. This process can weaken the metal, causing structural damage over time.

To understand this better, think of a metal can left outside. Eventually, a reddish-brown layer forms on its surface. This layer is rust, and it indicates that the iron in the can has combined with oxygen from the air or water. Preventing rust can involve painting the metal, using stainless steel, or coating the surface with oil or grease.

Boiling Water

Boiling water might seem straightforward, but the science behind it is quite fascinating. When you heat water, the molecules gain energy and move faster. Once the water reaches its boiling point, the water molecules have enough energy to change from a liquid to a gas.

This transition is called vaporization, and specifically, when it happens at the surface of a liquid, it's called boiling. This is a physical process because while the state of the water changes from liquid to gas, the composition remains H2O. The bubbles you see are actually pockets of water vapor. Boiling water is used for cooking, sterilization, and even driving turbines in power plants.

Pulverizing Substances

Pulverizing substances, such as grinding up an aspirin, involves breaking down a material into powder or tiny pieces. It is a physical process because it changes the form but not the essential nature or the chemical composition of the substance.

Why do we pulverize substances? It can increase the surface area, making them dissolve faster in liquids or react more quickly in chemical processes. Pharmacists, for instance, often pulverize medications to make them easier to ingest or to create a specific dosage.

Digestion of Food

The digestion of food is a complex dance of chemical reactions. Eating a candy bar isn’t simply about savoring the flavor; it’s about breaking down sugars, fats, and proteins into smaller molecules that our body can use.

Enzymes in our saliva start breaking down complex carbohydrates even before they reach our stomach. Proteins and fats meet their match with stomach acids and other digestive enzymes. This process transforms food into nutrients and energy, highlighting just how amazing our bodies are as natural chemical reactors.

Chemical Reactions

Chemical reactions are the heart of chemistry. They occur when substances interact to form new compounds, often with distinctly different properties. An explosive example is nitroglycerin, which, when detonated, decomposes rapidly in a chemical reaction that releases gases like nitrogen and carbon dioxide along with a great deal of energy.

These reactions can be slow, such as the rusting of iron, or extremely fast, like an explosion. They're integral to countless processes, from the industrial synthesis of chemicals to the metabolic pathways in our bodies. Understanding chemical reactions is essential not only for scientists but for everyone, as they are all around us, even in the very air we breathe.