Question

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Answer 1

1. A cold glass is left sitting outside on a hot day. Soon, water droplets form on the outside of the glass. Describe the events that must occur for the water droplets to form on the glass.

2. A glass of water sitting in direct sunlight evaporates over time. Explain this phase change in terms of the types of heat transfer that occur.

Answer 2

As long as the glass is colder than the water vapor's dew point, it will condense to liquid form that forms on the outside of the glass and since surface of the glass is a lot cooler than the surrounding air.

Warm moist air carries invisible molecules of water. When air gets colder it compresses (and if air gets hotter it expands, its volume increases).

As the air cools, at a certain point the water molecules are unable to stay in the air as invisible 'gas' (water vapour), and they change their state from gas to liquid. 'Liquid' is a more condensed form than a gas. The molecules are closer together in liquids than they are in their gas form/state. If warm moist air meets the side of an icy glass, the water vapour in that bit of air 'condenses' into a liquid (water) on the side of the glass.

Answer 3

2. During evaporation energetic molecule leave liquid phase lowering average energy of other liquid molecules. Remaining absorb energy from surrounding getting enough energy to enter into gas phase.
Evaporation depends on number of factors like surface area, inter molecular attractions and kinetic energy of particles.
Since the kinetic energy of a molecule is proportional to its temperature, evaporation proceeds more quickly at higher temperatures. As the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid, thus, decreases.


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