PhysicsLAB: Change of Phase

All matter can exist in the solid, liquid, or gaseous phases. The solid phase exists at relatively low temperatures, the liquid phase at higher temperatures, and the gaseous phase at still higher temperatures. Water is the most common example, not only because of its abundance but also because the temperatures for all three phases are common.



latent heat (phase change - no temperature change)

fusion (melting point)		Q = mL_f

vaporization (boiling point)		Q = mL_v

specific heat (temperature change within a phase)

(any phase)		Q = mcΔT

Refer to the following information for the next four questions.

Constants for Water

Ice	c = 2.10 J/gK	Fusion	L_f = 334 J/g
Water	c = 4.19 J/gK	Vaporization	L_v = 2260 J/g
where: J ≡ Joule, g ≡ grams, K ≡ Kelvin

a. How many joules are needed to change 1 gram of 0ºC ice to water at 0ºC?

b. How many joules are needed to change the temperature of 1 gram of water by 1ºC?

c. How many joules are needed to melt 1 gram of 0ºC ice and turn it to water at a room temperature of 23ºC?

d. How many joules are needed to change 1 gram of 100ºC boiling water to 100ºC steam?

Refer to the following information for the next three questions.

A 50-gram sample of ice at 0ºC is placed in a glass beaker that contains 200 g of water at 20ºC.

a. How much heat is needed to melt the ice?

b. By how much would the temperature of the water change if it gave up this much heat to the ice?

c. What will be the final temperature of the mixture? (Disregard any heat absorbed by the glass or given off by the surrounding air.)

Refer to the following information for the next two questions.

Fill in the number of joules at each step below for changing the state of 1 gram of 0º ice to 100ºC steam.

Why is it difficult to make tea on the top of a high mountain?

Refer to the following information for the next three questions.

One gram of steam at 100ºC condenses, and the water cools to 22ºC

a. How much heat is released when the steam condenses?

b. How much heat is released when the water cools from 100ºC to 22ºC?

c. How much heat is released altogether?

Refer to the following information for the next three questions.

In a household radiator 1000 g of steam at 100ºC condenses, and the water cools to 90ºC.

a. How much heat is released when the steam condenses?

b. How much heat is released when the water cools from 100ºC to 90ºC?

c. How much heat is released altogether?

Refer to the following information for the next question.

To get water from the ground, even in the hot desert, dig a hole about a half meter wide and a half meter deep. Place a cup at the bottom. Spread a sheet of plastic wrap over the hole and place stones along the edge to hold it secure. Weigh the center of the plastic with a stone so it forms a cone shape.

Why will water collect in the cup? (Physics can save your life if you're ever stranded in a desert!)