Question

State whether each of the following is a physical or a chemical change: (a) slicing an orange into wedges (b) fermenting apples into apple cider (c) grinding sugar crystals into powder (d) digesting carbohydrates for energy

Short answer

(a) Physical change, (b) Chemical change, (c) Physical change, (d) Chemical change.

Step-by-step solution

Understand Physical vs Chemical Change

A physical change is a change in the form or physical properties of a substance, without a chemical reaction or the formation of a new substance. A chemical change involves a chemical reaction, with new substances being formed and energy often being released or absorbed.

Analyze Each Scenario

We will determine the type of change for each scenario by checking if there's a formation of new substances.

Slicing an Orange into Wedges

Slicing an orange involves cutting it into smaller pieces. No new substances are formed, so this is a physical change.

Fermenting Apples into Apple Cider

During fermentation, yeast or bacteria convert sugars in the apples into alcohol (ethanol). This forms new substances, making it a chemical change.

Grinding Sugar Crystals into Powder

Grinding sugar changes its physical appearance (from crystals to powder), but no new substances are formed. Hence, this is a physical change.

Digesting Carbohydrates for Energy

Digestion breaks down carbohydrates into simpler molecules and involves chemical reactions within the body, forming new substances. This is a chemical change.

Key concepts

Physical Change

A physical change occurs when the form or appearance of matter is altered. However, its chemical composition remains the same. This means that no new substances are formed. Physical changes are usually reversible, meaning you can return the matter to its original state.

• For example, slicing an orange into wedges represents a physical change. The orange remains composed of the same chemical substances, just in smaller pieces.
• Likewise, grinding sugar crystals into powder alters its appearance but not its molecular structure. The sugar's chemical identity remains unchanged as well.

Physical changes can be as simple as changes in shape, size, or state (like melting or freezing), but without changing the chemical identity of the substance.

Chemical Change

Chemical changes result in the formation of one or more new substances with new chemical properties. These changes involve chemical reactions where the original substances' molecular structures are rearranged.

• For instance, fermenting apples into apple cider is a chemical change. The sugars in the apples are transformed into alcohol and carbon dioxide, creating substances with different molecular compositions.
• The digestion of carbohydrates for energy also exemplifies a chemical change. Enzymes in the body break down carbohydrates into simple sugars, producing new molecules suitable for cellular energy production.

Chemical changes are often irreversible under normal conditions and may involve noticeable changes such as gas production, color changes, or the release or absorption of energy.

Matter Transformations

Matter transformations entail changes in matter that can be categorized as either physical or chemical. Understanding these transformations is key to mastering concepts in chemistry.

• Physical transformations include changes that affect the state or form of matter without altering its chemical composition. This includes processes like evaporation, condensation, or simple physical deformation.
• Chemical transformations, on the other hand, involve changes at the molecular level resulting in new chemical entities. Examples include oxidation, fermentation, and combustion.

Grasping the differences between physical and chemical transformations allows students to predict and explain the outcomes of different processes and reactions observed in both natural and laboratory settings.