Question

Which of the following is/are examples of a chemical change? a. carving wood b. snow melting c. dry ice subliming (solid \(\mathrm{CO}_{2}\) vaporizing into a gas, passing the liquid state) d. burning cookies in the oven

Short answer

The correct answer is option (d) burning cookies in the oven, as it involves a chemical change due to the formation of new chemical compounds during the process. The other options (a, b, and c) are physical changes as they do not involve any change in the chemical composition of the substances.

Step-by-step solution

Analyze the given options

First, let's analyze each option individually to understand its nature (chemical or physical change): a. Carving wood is the process of shaping and cutting wood, which does not change the chemical composition of the wood. It only alters the physical appearance of the wood. b. Snow melting involves a change in the state of water, from solid (ice) to liquid. The chemical composition of water (H2O) remains the same during this process, so it is a physical change. c. Dry ice subliming is the process in which solid carbon dioxide (CO2) directly turns into a gaseous state, without going through the liquid phase. Although the physical state changes, the chemical composition (CO2) remains the same, meaning it is a physical change. d. Burning cookies in the oven causes the cookies to undergo chemical reactions due to the heat. During the process, many new chemical compounds are formed, such as carbon and water, leading to a change in the chemical composition of the cookies.

Determine the correct answer

Now that we have analyzed all the given options, we can determine the correct answer. Out of the four options: - Carving wood is a physical change. - Snow melting is a physical change. - Dry ice subliming is a physical change. - Burning cookies in the oven is a chemical change. So, the correct answer is option (d) burning cookies in the oven, which is a chemical change.

Key concepts

Physical Change

When we talk about a physical change, we are referring to a transformation that affects the form or appearance of a substance but does not alter its chemical composition. This type of change is generally reversible. For instance, when snow melts, it is simply water changing from its solid state, ice, to its liquid state. Similarly, when dry ice sublimes, it's carbon dioxide moving from solid to gas. These are examples of physical changes because they only involve a change in the state of matter of the substances.

• Solid ice melting into liquid water.
• Breaking a piece of chalk.
• Whipping egg whites to create foam (air is trapped creating a new texture but the egg whites are chemically the same).

In a homework or exam situation, recognizing a physical change can be simplified by asking yourself if the substance could be returned to its original state. If the answer is 'yes', then it is likely a physical change.

State of Matter

The concept of a state of matter is fundamental in understanding physical changes. Matter can exist in different states—solid, liquid, gas, and plasma—each with unique physical properties.

For example, water is unique because at Earth’s normal pressures it can naturally be found in all three common states of matter: as ice (solid), water (liquid), and steam (gas).

Important to remember:

• Solids have a fixed shape and volume.
• Liquids have a fixed volume but can take the shape of their container.
• Gases have neither fixed shape nor volume, expanding to fill their container.

Phenomena like melting, boiling, freezing, and sublimation are physical processes that signify a change in the state of matter. The molecules in these substances are rearranging themselves, but they are not changing their fundamental structure.

Chemical Composition

Exploring the concept of chemical composition leads us to understanding chemical changes. When a substance undergoes a chemical change, its molecular structure is altered, creating new substances with different properties from the original. These changes often result from chemical reactions and are usually irreversible.

A classic example of an alteration in chemical composition is the burning of cookies in an oven, like in our exercise. The heat causes the ingredients to react chemically and transform into new substances like carbon and water vapor.

Other common examples include:

• Rusting of iron.
• Baking a cake.
• Digesting food.

Chemical changes can be spotted by changes in color, temperature, formation of a precipitate, or the emergence of gas bubbles. In a study context, to confirm if a chemical change has occurred, look for evidence of a new substance formed as a result of the reaction.