Temperature and Heat

1. Temperature and Heat

2. Watch It Spread Overview For this introductory activity you will observe food coloring after it is placed into water of various temperatures. • Hypothesis: ? • Materials: • food coloring • three 250 mL beakers • water of various temperatures (hot, room temperature, cold) • clock/timer • data table • Procedures: • Write a hypothesis on the back of your data table. • Label the beakers and fill them with 100 mL of hot, room temperature, and cold water. • Place a drop of food coloring into each of the beakers. • Each member of the group should rate how much the food coloring has diffused in the beaker over a ten minute period of time: • 1 = small amount (≈1-33%) • 2 = medium amount (≈33-67%) • 3 = large amount (≈67-100%). • Average your results and create a line graph of your average data with the rating on the y-axis and the timed intervals on the x-axis. Do not touch/move the beakers once the water and food coloring are in them.

3. Data Table

4. Discussion Questions • What patterns or trends did you notice? • What factors could have impacted the accuracy of your data? • Did your data support your hypothesis? Explain your reasoning.

5. Kinetic Theory of Matter • states that all of the particles that make up matter are constantly in motion  all particles in matter have kinetic energy • energy is transferred when particles collide with one another • helps explain the different states of matter • PhET What do you think happens when a slow moving particle is struck by a fast moving one?

6. Temperature • the quantity that tells how hot or cold something is compared to a standard • the average kinetic energy of all the particles in an object  not determined by how much of a substance you have • Higher average kinetic energy (particle movement) results in higher temperatures, while lower average kinetic energy (particle movement) results in lower temperatures • measured using a thermometer

7. Thermometer • an instrument for measuring temperature • typically a thin glass tube filled with a liquid (alcohol or mercury) • mercury is not typically used anymore because of its impact on the environment • works because of thermal expansion • consist of three different scales: • Fahrenheit (0F) • Celsius (0C) • Kelvin (K) Why is alcohol used in thermometers instead of water?

8. Temperature Scales Which scale is being represented by each thermometer? 2120 1000 373 Water boils The Kelvin scale does not have negative numbers 680 200 293 Room temperature 320 00 273 Water freezes Fahrenheit Celsius Kelvin

9. Example Example Example Example 0F = 9 x 0C + 32 5 = 9 x + 32 5 Converting Between Scales • Celsius to Fahrenheit • Fahrenheit to Celsius • Celsius to Kelvin • Kelvin to Celsius 50C 0F 410F 0F 50C 0C 700F 0C 0C = 5 x (0F - 32) 9 = 5 x ( - 32) 9 210C 0C 700F 0F 100C K K = 0C + 273 283K 100C K 0C = + 273 100 K 0C -1730C 0C 100 K K 0C = K - 273 = - 273

10. Combining Different Temperatures Overview For this activity you will mix different amounts of hot and cold water. • Materials: • 3 - 250 mL beakers • 2 - 100 mL graduated cylinder • three Celsius thermometers • hot and cold water • Procedures: • Label the three beakers (H, C, M). • Using the graduated cylinder, measure the amount of cold water specified by the data table and pour it into the beaker labeled “C.” Measure and record the temperature. • Using the graduated cylinder, measure the amount of hot water specified by the table and pour it into the beaker labeled “H.” Measure and record the temperature. • Predict what the temperature will be after combining the beakers. • Pour the hot and cold water into the beaker labeled “M.” Measure and record the water temperature. • Repeat steps 2-5 for the remaining mixtures specified by the data table.

11. Data Table

12. Questions • How does the temperature of the different mixtures compare to the original temperatures of the water? • For which mixture did your prediction come closest? • For which mixture was your prediction farthest off? • Could the temperature of the mixture (hot and cold) ever reach the temperature of the hot or cold water? Explain your reasoning. • Although the hot water was the same temperature in each beaker, the impact observed when it was combined with the cold water varied. Why did they all have a different effect? • What factors could have impacted the accuracy of your data? • What did you learn about mixing temperatures from this activity? • What would you predict the temperature to be if 200 mL of hot water (≈1000C) is mixed with 50 mL of cold water (≈00C) ? Explain your reasoning.

13. Heating and Cooling a Metal Strip • Plug in the hot plate and allow it to heat up for 3-5 minutes. • Have a conversation with the members of your group regarding what you think will happen once you heat and cool the metal strip. • Using the hot plate, heat the metal strip with the printed side facing upward. It is not necessary to touch the metal strip on the hot plate. • Take note of what you observe as the metal strip is heated with the hot plate. • Allow the strip to cool for a few minutes. • Gently rub the metal strip on an ice cube with the printed side facing upward. • Take note of what you observe as the metal strip is being cooled with the ice.

14. Discussion Questions • What observations did you make after putting the metal strip over the hot plate? Be specific!!! • Why/how did this happen? • What observations did you make after rubbing the metal strip on the ice cube? Be specific!!! • Why/how did this happen? • What do you think would have happened if it was heated or cooled to a greater degree? The metal strip is actually know as a bimetal strip.

15. Thermal Expansion • the increase in volume of a substance due to an increase in temperature – the particles themselves DO NOT expand • as a substance gets hotter the particles move faster and spread out • most matter expands when it’s heated and contracts when it’s cooled • Exception - water actually expands as it cools from 40C to 00C • different substances expand at different rates • gases generally expand or contract more than liquids, and liquids expand or contract more than solids • Example: • Bimetal strips in thermostats As the particles spread out, the volume of a substance increases. What happens to the substance’s density?

16. Piece of Metal Thermal Expansion & Contraction(A closer look) Expansion Contraction

17. Applications of Thermal Expansion and Contraction Try to apply and/or explain the concepts of thermal expansion and contraction as they pertain to the following examples. • expansion joints in bridges or sidewalks • thermometers • hard to open jar lid • railroad tracks and train derailments • telephone/power lines • potholes • objects filled with gas (tire, balloon, athletic ball, etc.) What are some personal examples or experiences with thermal expansion and contraction?

18. Heat • flow or transfer of energy from an object at a higher temperature to an object at a lower temperature, until thermal equilibrium is reached • matter does not have heat, it has thermal energy • typically expressed in units of joules (J) and calories (cal) • Calorie is really a kilocalorie and represents food energy • 4.187 joules = 1 calorie • scientists believed that heat was an invisible, weightless fluid capable of flowing caloric • Count Rumford (Benjamin Thompson) challenged the idea of caloric when he discovered that heat was being produced when holes were drilled into cannon barrels • 3 types of heat transfer: conduction, convection, radiation Why does an ice cube feel cold while a paper cup filled with coffee feels hot? Boiling Water in a Paper Cup

19. Using the Conductometer • Place an equal amount of wax in the divots of each rod (A,B,S,N,C). • Light the candle. • With the wax filled divots facing upward, place the central heating disk directly over the candle. • Observe the order in which the wax melts.

20. Discussion Questions • What is the order in which the wax melts. • What impacted how quickly the wax melted in each rod? • What factors could have impacted the accuracy of your results? • Copper (C) • Aluminum (A) • Brass (B) • Steel (S) • Nickel (N)

21. Specific Heat Capacity • the amount of energy needed to change the temperature of 1 kg of a substance by 10C • how easily substances change temperatures • increases as the size of the particles that make up the substance increase • the higher the value  the more energy and the longer it takes to heat up or cool down • e.g. – with a specific heat of 0.11 cal/g0C (444 J/kg0C), nickel will take longer to heat up and cool down compared to copper which has a specific heat value of 0.09 cal/g0C (387 J/kg0C) • can be used to help calculate heat lost or gained by a substance • formula: mc∆T Explain how/why bodies of water in our area are warmer towards the end of the summer compared to the beginning.

22. Table of Specific Heat Values

23. Thermal Energy vs. Temperature vs. Heat

24. Conduction • transfer of thermal energy through a substance, or from one substance to another by direct contact of particles • takes place in solids, liquids, and gases, but takes place best in solids because the particles of a solid are in direct contact with each other Unfortunately for someone, after being touched, the heat will transfer from the iron to the hand. What are some other real-life examples where heat is transferred by conduction?

25. Conductors substances that conduct thermal energy well particles are close together different metals are common conductors Insulators substances that do not conduct thermal energy well  they delay heat transfer particles are far apart different plastics are common insulators Conductors and Insulators What are some common conductors and insulators? Melting Blocks

26. Convection • transfer of thermal energy through fluids (liquids or gases) by means of up and down movements called convection currents • the circular motion of liquids or gases due to density differences that result from temperature differences As the air gets heated by the flame, the particles move faster and spread out. This increases the volume of the air inside the balloon, which lowers the density. This decrease in density causes the balloon to rise. Sea and land breezes result from uneven heating of the Earth’s surface and the resulting convection currents. Explain how this happens.

27. Radiation • transfer of thermal (radiant) energy as electromagnetic waves, such as visible light or infrared waves • energy can be transferred through matter or empty space • darker objects absorb more radiant energy than lighter objects Notice how the visible light from the sun travels through space and heats the Earth.

28. 387 J kg·C Calculating Heat – Sample Problem • How many joules are needed to raise the temperature of 100 kilograms of copper from 10 C to 100 C? The specific heat of copper is 387 J/kg·C. Take the difference between 100C and 1000C Q = mc∆T specific heat heat mass change in temperature Heat = (100 kg) (90 C) Heat = 3,483,000 J