Question

The boiling of water is a a. physical change because the water disappears. b. physical change because the gaseous water is chemically the same as the liquid. c. chemical change because heat is needed for the process to occur. d. chemical change because hydrogen and oxygen gases are formed from water. e. chemical and physical change. Explain your answer.

Short answer

The boiling of water is a physical change because the gaseous water is chemically the same as the liquid. This occurs as the water changes from a liquid state to a gaseous state without any alteration in the chemical composition, only due to the addition of heat. So, the correct answer is option b.

Step-by-step solution

Examine each option

Let's analyze each given answer option and determine which one correctly identifies the boiling of water as either a physical or chemical change. a. physical change because the water disappears. - This statement is incorrect. While the boiling of water is indeed a physical change, the change is not described appropriately. Water doesn't disappear, it changes from liquid to gas state. b. physical change because the gaseous water is chemically the same as the liquid. - This statement can be true. When water boils, it changes from a liquid to a gas - steam or water vapor. The chemical composition of water remains the same in both states, which means that it is a physical change. c. chemical change because heat is needed for the process to occur. - This statement is incorrect. While heat is necessary for the boiling process, it doesn't mean the change is chemical. Physical changes can also require heat. d. chemical change because hydrogen and oxygen gases are formed from water. - This statement is incorrect. When water boils, it changes its state from a liquid to a gas, but the chemical composition remains the same - H₂O. Hydrogen and oxygen gases are not formed during the boiling process. e. chemical and physical change. - This statement is incorrect because a process cannot be both chemical and physical changes. Boiling water is either physical or chemical, not both.

Choose the correct answer

Based on our analysis, the correct answer is: b. physical change because the gaseous water is chemically the same as the liquid. The boiling of water is a physical change because it changes from a liquid state to a gaseous state without any change in the chemical composition. The process doesn't alter the chemical properties of water but merely changes its state due to the addition of heat.

Key concepts

Boiling

Boiling is a fascinating and common phenomenon that occurs when a liquid turns into vapor. It's the point at which the liquid heats up enough for bubbles to form and rise to the surface, turning into gas. In the case of water, this happens at 100°C (212°F) at sea level. During boiling, the temperature of a liquid remains constant even though heat continues to be applied. This is because the added energy is used to transform the liquid into gas rather than increasing its temperature further.

Boiling is unique because it triggers a visible change in form: the water undergoes a state transition from liquid to gas, commonly referred to as steam or water vapor. This marks an exciting stage of learning why certain factors like atmospheric pressure can affect the boiling point. It's a useful process in cooking and sterilization, demonstrating a basic principle of physics related to heat and energy transfer.

Water

Water is a remarkable substance that covers a major part of our planet and constitutes a large part of all living organisms. Chemically, water is denoted as H₂O, which signifies each molecule comprises two hydrogen atoms covalently bonded to one oxygen atom. This precise chemical structure gives water its unique properties, including its ability to exist in three states: solid (ice), liquid (water), and gas (vapor).

Water's capacity to change state without altering its fundamental chemical makeup is pivotal in many natural processes and human activities. Its role as a solvent, in hydration, and as a medium for biochemical reactions makes it indispensable. The chemical stability of water demonstrates why its phase changes, like boiling, are classified as physical changes rather than chemical transformations.

State Change

State change is a key concept in understanding how matter transitions between solid, liquid, and gaseous forms. These changes are physical because they don't involve altering the chemical structure of the substance. For water, the transition from liquid to vapor during boiling is an example of a state change.

Understanding state changes involves grasping the concepts of melting, freezing, vaporization (which includes both evaporation and boiling), condensation, and sublimation. Each of these processes requires energy, typically in the form of heat, to break intermolecular forces without changing the substance's chemical identity. This is why during the boiling of water, the change involves energy input to transform liquid molecules into gas while keeping H₂O chemically intact.

Chemical Composition

Chemical composition refers to the types and proportions of atoms that compose a chemical or a substance. For water, its chemical composition is consistently H₂O whether it's in solid, liquid, or gas form. This consistent composition is why physical changes like boiling don't involve changes at the molecular level between hydrogen and oxygen atoms. The bonds between these atoms remain intact during such transitions.

Contrastingly, a chemical change would result in the rearrangement of these atoms, forming new substances entirely. That's not what happens in boiling; instead, it involves molecules gaining enough energy to overcome atmospheric pressure and transition to a gaseous state, all while retaining the molecular structure of water.

Heat

Heat plays a crucial role in the boiling process, providing the essential energy required for state changes. When water is heated, its molecules begin to move more rapidly, leading to an increase in kinetic energy. Upon reaching boiling point, these molecules have gathered enough energy to break free of the liquid phase, transitioning into vapor.

It's important to note that while heat is crucial, the process remains a physical change because the chemical identity of water doesn't alter. Instead, heat facilitates the transformation by breaking intermolecular forces but not chemical bonds. Understanding how heat influences states of matter helps to distinguish between physical and chemical changes, further clarifying key scientific concepts about energy transfer and matter dynamics.