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 nitroglycerin.

Short answer

(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 (e) Exploding of nitroglycerin: Chemical process

Step-by-step solution

(a) Rusting of a metal can

Rusting of a metal can is the result of a reaction between the metal's surface and oxygen in the presence of moisture. This reaction leads to the formation of a new compound, called iron(III) oxide or rust. Since the chemical composition of the metal changes, this is a chemical process.

(b) Boiling a cup of water

Boiling a cup of water involves heating up water until it turns into its gaseous form - water vapor. The process does not involve any change in the chemical composition of water - it just changes from its liquid state to the gaseous state. Thus, this is a physical process.

(c) Pulverizing an aspirin

Pulverizing an aspirin involves breaking apart the aspirin tablet into smaller particles or powder. This process does not involve any change in the chemical composition of the aspirin itself. It merely changes the physical form of the substance, from a solid to a powder. Therefore, this is a physical process.

(d) Digesting a candy bar

Digesting a candy bar involves a series of chemical reactions that occur within our bodies. The food is broken down into simpler, smaller molecules that can be absorbed and used by the body. The process involves a change in the chemical composition of the candy bar, making it a chemical process.

(e) Exploding of nitroglycerin

The explosion of nitroglycerin involves a rapid decomposition of the nitroglycerin molecules, releasing a large amount of energy in the form of heat and pressure. This process involves a change in the chemical composition of nitroglycerin, as it breaks down into simpler molecules. Therefore, this is a chemical process.

Key concepts

Physical Process

A physical process involves changes in the state or appearance of a substance but does not alter its chemical composition. Examples of physical processes include changes in physical states such as solid, liquid, and gas.
For instance, when you boil water, its state changes from liquid to gas but it remains H₂O in its chemical structure. Likewise, pulverizing aspirin only changes its physical form from tablet to powder, but the chemical makeup of aspirin itself stays the same.

• State changes: solid, liquid, gas
• No change in chemical composition
• Examples include boiling, melting, crushing

Rusting

Rusting is a specific type of chemical process where metal, particularly iron, reacts with oxygen and moisture from the environment to form iron(III) oxide, commonly known as rust. This reaction occurs over time and degrades the metal, creating a layer of reddish-brown rust.
The process of rusting is a slow chemical change that requires the presence of water or humidity to facilitate the reaction between iron and oxygen. This is why metal left exposed to the elements often rusts faster.

• Involves iron and oxygen
• Formation of iron(III) oxide
• Causes degradation of metal

Chemical Reaction

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. It involves breaking and forming bonds between atoms. For example, rusting or burning are both chemical reactions where new compounds are formed.
In a chemical reaction, the reactants' molecules transform into products with different chemical properties. This transformation is what characterizes a chemical reaction.

• Transformation at molecular level
• Involves breaking/forming chemical bonds
• Creation of substances with new chemical properties

Boiling

Boiling is a physical process where a liquid turns into vapor when its temperature reaches the boiling point. This process does not involve altering the liquid's chemical structure. For instance, boiling water transforms liquid water into water vapor, but it remains H₂O.
The boiling process involves heat which provides the energy required for molecules in the liquid to break free and form gas, allowing substances to change states without undergoing any chemical changes.

• Phase change: liquid to gas
• No change in chemical composition
• Temperature-dependent process

Digesting

Digesting is a chemical process where the body breaks down food into smaller, absorbable molecules through a series of enzymatic reactions. This involves both mechanical and chemical breakdown starting from the mouth and continuing through the digestive tract.
During digestion, enzymes like amylase, protease, and lipase catalyze reactions that convert carbohydrates, proteins, and fats into simpler molecules that can be absorbed by the body for energy and nutrients.

• Enzymatic breakdown of food
• Transformation of food into absorbable molecules
• Involves both mechanical and chemical processes

Explosion

An explosion is a rapid and violent chemical reaction that releases a large amount of energy in a short time frame. It involves the decomposition or transformation of substances, like nitroglycerin, into simpler molecules with a sudden release of gas and heat.
The speed and energy output of the reaction make explosions distinct from other types of chemical reactions. These reactions are characterized by rapidly expanding gases which can cause damage due to high pressure and sound waves.

• Rapid chemical transformation
• High energy and gas release
• Can result in pressure and shock waves