Questions and Answers
What process involves the direct change from solid to gas?
Boiling is a surface phenomenon.
False
What is the heat energy required to change 1 kg of a liquid to gas at its boiling point called?
Latent heat of vaporisation
The process of changing from gas to solid without going through the liquid state is called _____?
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Match the process with its definition:
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Which of the following factors does NOT affect the rate of evaporation?
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What is the phenomenon called when a liquid changes into vapour below its boiling point?
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Humidity refers to the absence of water vapour in the air.
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How does an increase in wind speed affect the rate of evaporation?
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The particles of liquid absorb __________ from the surrounding during evaporation.
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Match the following states of matter with their properties:
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Which of the following is a factor affecting the rate of evaporation?
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Evaporation can occur at any temperature.
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What happens to the particles at the surface of a liquid during evaporation?
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At what temperature does water boil and begin to change from a liquid to a vapor?
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The rate of evaporation decreases with an increase in surface area.
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What happens to water when it is left uncovered?
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The process by which a liquid changes into vapor without reaching the boiling point is called ______.
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Which of the following factors does NOT influence the rate of evaporation?
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Particles of matter are always at rest.
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Match the physical states of matter with their properties:
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What effect does an increase in temperature have on the particles in a liquid?
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Study Notes
Physical State of Water
- At 250°C, water is in a gaseous state (steam).
- At 100°C, water can coexist in both liquid and gaseous states; it boils at this temperature.
Constant Temperature During Change of State
- Temperature remains constant during a change of state due to the energy being used to change the state rather than increasing temperature.
- Energy is absorbed or released during phase changes, maintaining constant temperature until the state transition is complete.
Factors Affecting Evaporation
- Surface Area: Increased surface area elevates the rate of evaporation as more particles are exposed to atmospheric conditions (e.g., spreading out wet clothes aids in drying).
- Temperature: Higher temperatures enhance kinetic energy of particles, allowing more of them to escape into the vapor state.
- Humidity: High humidity reduces evaporation rates because air is already saturated with water vapor, limiting additional evaporation.
- Wind Speed: Increased wind speed accelerates evaporation by removing water vapor from the area around evaporating surfaces, promoting further evaporation (e.g., clothes dry faster on windy days).
Evaporation and Cooling
- Evaporation is a cooling process; as liquid particles evaporate, they absorb energy, cooling the remaining liquid.
- For example, when water evaporates from a surface, the surface loses heat, leading to a cooling effect.
Key Concepts of Phase Changes
- Sublimation: Transition from solid directly to gas without becoming liquid (e.g., dry ice).
- Deposition: Transition from gas directly to solid without becoming liquid (e.g., frost formation).
- Boiling vs. Evaporation: Boiling is a bulk phenomenon occurring at the boiling point, whereas evaporation occurs at any temperature and involves only surface particles.
Heat Energy Concepts
- Latent Heat of Vaporization: Heat energy required to convert 1 kg of liquid to gas at its boiling point under atmospheric pressure.
- Latent Heat of Fusion: Heat energy needed to change 1 kg of solid to liquid at its melting point.
Kinetic Energy and Evaporation
- Liquids consist of particles with varying kinetic energy; only those with sufficient energy can escape liquid's surface to evaporate.
Experimental Observation
- Conducting activities (like placing water in a test tube near air flow) illustrates evaporation and cooling as surrounding energy is absorbed during the phase transition.
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Description
Explore the physical states of water at various temperatures such as 250°C and 100°C. This quiz examines the effects of temperature, surface area, and wind on the state changes of substances, enhancing your understanding of physical properties.
