1 of 21

TEMPERATURE, HEAT, AND PHASE CHANGES

Vincent van Gogh

Landscape with Wheat Sheaves and Rising Sun

2 of 21

PHASE CHANGES

  • Phase changes occurs when enough energy is added to a substance (endothermic process) or released by the substance (exothermic process) that the intermolecular forces change enough to form a new phase.

3 of 21

PHASE CHANGES

​

Solid → Liquid → Gas

Endothermic

Weaker Intermolecular Forces

4 of 21

PHASE CHANGES

​

Gas → Liquid → Solid

Exothermic

Stronger Intermolecular Forces

5 of 21

PHASE CHANGES

States Changing

Phase Change Name

Endothermic or Exothermic

Solid → Liquid

Melting

Endothermic

Liquid → Solid

Freezing

Exothermic

Liquid → Gas

Vaporization

Endothermic

Gas → Liquid

Condensing

Exothermic

Solid → Gas

Sublimating

Endothermic

Gas → Solid

Deposition

Exothermic

6 of 21

HEATING CURVE

7 of 21

HEATING CURVE

8 of 21

TEMPERATURE DEPENDS ON PARTICLE MOVEMENT!

  • All matter is made up of atoms that are moving (have kinetic energy)…even solid objects have atoms that are vibrating.
  • The motion from the atoms gives the object energy.
    • Solid = vibrate (jiggle) but do not move from place to place.
    • Liquid = vibrate but can slide past each other.
    • Gas = vibrate and move independently at high speeds.

Solid

Liquid

Gas

9 of 21

TEMPERATURE

  • Temperature: The measure of the average kinetic energy of all the particles in the object
  • KE = ½ mv2
  • TK = TC + 273

10 of 21

HOW DOES A THERMOMETER WORK?

A thermometer can measure temperature because the liquid inside expands (rises) when heated or contracts (lowers) when cooled by a linear amount.

11 of 21

THERMAL EXPANSION

  • All gases, liquids, and most solids (water is the exception) expand when their temperature increases.

​

  • This is why bridges are built in short segments with small breaks to allow for expansion.

Expansion joints such as this one are used in bridges to accommodate thermal expansion.

12 of 21

THERMAL ENERGY

If each of the objects to the right is the same temperature, which has more thermal energy?

the total kinetic energy of particles in an object.

13 of 21

LET’S TALK ABOUT TEMPERATURE

14 of 21

TOUCH THE TWO OBJECTS�STYROFOAM BLOCK VS. METAL BLOCK

  • Which has the higher temperature?
  • How do you know?
  • What does that mean?
  • What about the temperature of the room? Both objects are in this room.
  • Let’s measure the temperature of the two objects with an infrared thermometer...
  • Whoa! Why do the two object feel different but are the same temperature?

15 of 21

ICE ON THE TWO OBJECTS

  • If ice is placed on both of the objects, what will happen?
  • Let’s try!
  • Whoa...what happened and why?

16 of 21

WHY DID THE METAL FEEL COLDER THAN THE STYROFOAM?

  • The metal transferred heat faster than the Styrofoam.
  • Why would this make the metal feel colder (a lower temperature?)

https://www.youtube.com/watch?v=vqDbMEdLiCs

17 of 21

ENERGY FLOWS FROM WARMER TO COOLER OBJECTS (ALWAYS!)

  • Heat: the flow of energy from a substance at a higher temperature to a substance at a lower temperature.

Example: Placing a cold spoon in hot water

18 of 21

MEASURING HEAT

What are the units of heat?

  • calorie (cal): The amount of energy needed to raise the temperature of 1 gram of water by 1oC
  • Joule (J): the SI unit of energy

​

  • 1.00 calorie= 4.18 J

19 of 21

SOME SUBSTANCES CHANGE TEMPERATURE MORE EASILY THAN OTHERS.

Specific Heat:

the amount of energy required to raise the temperature of 1 gram of a substance by 1oC

20 of 21

SOME SUBSTANCES CHANGE TEMPERATURE MORE EASILY THAN OTHERS.

  • Substances with a lower specific heat require less energy to change their temperature.
  • Substances with a higher specific heat require more energy to change their temperature.

21 of 21

WHY DID THE METAL FEEL COLDER THAN THE STYROFOAM?

  • The metal had a lower specific heat than the styrofoam so the metal transferred heat faster than the styrofoam.
  • Why would this make it feel colder (a lower temperature?)