Heat & Temperature
What is the direction of heat flow when an ice pack is placed on your skin?
From your warmer skin to the colder ice pack.
Which phase change is exothermic: melting, vaporization, condensation, or sublimation?
Condensation
On a heating curve, when temperature is increasing, what type of energy is increasing?
Kinetic energy
What is the formula used to calculate heat when temperature changes?
q = mcΔT
What phase change requires the heat of vaporization?
Liquid to gas (vaporization) or gas to liquid (condensation).
What does temperature measure?
The average kinetic energy of the particles
During boiling at 100°C, what happens to the potential energy of liquid water?
It increases.
What remains constant during a phase change on a heating curve?
Temperature and kinetic energy.
Water has a specific heat of 4.18 J/g·°C. What does that number mean?
It takes 4.18 J to heat 1 gram of water by 1°C.
What does the heat of fusion describe?
The amount of energy needed to change a substance from solid to liquid (or liquid to solid) at its melting point.
Convert 50 K to degrees Celsius.
–263°C
Which term describes a solid changing directly to a gas?
Sublimation
Which part of a cooling curve shows the gas condensing?
A horizontal (flat) segment above the boiling point.
How many joules are absorbed when 15.0 g of water warms from 14°C to 6°C?
-501.6 J
Is melting endothermic or exothermic, and why?
Endothermic, because energy is absorbed to break intermolecular forces.
What is absolute zero?
Absolute zero is the lowest possible temperature, where particles have no kinetic energy (no motion).
–273°C
–459°F
At which point on a heating curve does both solid and liquid exist?
At the flat segment during melting (plateau at melting point).
On a heating curve, what is happening to the potential energy and kinetic energy during a flat (horizontal) segment?
Potential energy increases while kinetic energy stays the same.
A 32.1 g sample of metal absorbs 67 J and increases 13 K. What is its specific heat?
0.161 J/g·K
How much energy is needed to melt 50.0 g of ice at 0°C?
16,700 J
Explain the difference between heat and temperature.
Heat is total energy that depends on sample size, while temperature is the average kinetic energy and does not depend on size.
During which process does potential energy decrease: freezing, boiling, melting, or evaporation?
Freezing
A substance is heated starting as a solid below its melting point. During which segment does the temperature remain constant but energy is still being absorbed, and why?
During the phase change (the flat segment), temperature stays constant because the absorbed energy is used to break intermolecular forces, increasing potential energy.
What mass of water is heated from 3°C to 80°C when it absorbs 4200 J?
13 g
A 25.0 g sample of water at 100°C is completely vaporized. How much energy is absorbed?
56,500 J