A physical transition from one state of matter to another caused by adding or removing thermal energy, during which the temperature remains constant while the energy goes into rearranging the particles (breaking or forming intermolecular attractions) rather than into raising or lowering temperature.
Add enough heat and a solid melts to liquid, then boils to gas. Remove heat and the reverse happens.
Showing a random 20 of 50 problems.
Example 1
medium
Why does an ice cube cool a drink?
Example 2
easy
Dew forms on grass overnight. Name the phase change.
Example 3
easy
What is the name of the phase change from solid to liquid?Name the phase change from solid to liquid.
Example 4
hard
Why does sweating cool the human body?
Example 5
easy
Water turns to ice. Which phase change is this?
Example 6
medium
At −10∘C snow can disappear without melting. Explain.
Example 7
medium
Identify the phase change: water vapor in warm air touches a cold glass and forms droplets.Water vapor touches a cold glass and forms droplets — name the phase change.
Example 8
easy
What is the phase change from gas to liquid called?Name the phase change from gas to liquid.
Example 9
hard
Calculate the heat needed to vaporize 25.0 g of water at 100 °C. Use Lv=2260J/g.
Example 10
medium
Order the energy requirement: which absorbs energy and which releases it: (a) freezing, (b) melting, (c) condensation?
Example 11
easy
What is the phase change from liquid to solid called?Name the phase change from liquid to solid.
Example 12
easy
What is the boiling point of water in °C at sea level?
Example 13
hard
Name the phase change that is the reverse of sublimation.
Example 14
easy
During boiling, the temperature of pure water stays at 100 °C. Why does the temperature not rise?At 100 °C, added heat drives the liquid-to-gas transition rather than raising temperature.
Example 15
challenge
On a phase diagram for water, what does the triple point represent, and approximately what temperature is it for water?
Example 16
easy
Name the six phase changes and indicate whether each absorbs or releases energy.All six phase changes connect solid, liquid, and gas states.
Example 17
easy
Is a phase change a physical change or a chemical change?
Example 18
medium
Name the phase change for each: (a) candle wax hardening, (b) puddle drying up, (c) ice cube shrinking in a freezer over weeks.
Example 19
medium
During freezing, do water molecules gain or lose energy?
Example 20
challenge
A heating curve for water shows two flat plateaus as you heat ice from -20 °C to steam. Explain what each plateau represents and why temperature is constant there.