2Objectives Define specific heat capacity. Solve problems involving specific heat capacities.Explain the difference between solid, liquid, and gaseous phases.Explain in terms of molecular behavior why temperature does not change during a phase change.Define latent heat.Solve problems involving latent heats.
3ActivitiesWorksheetLab demonstration: Determining the specific heat capacity of a substanceLab demonstration: Determining the latent heat of a substanceDesign lab: Design a homemade calorimeter and test it
4Specific heat capacity If heat flows into an object, its temperature rises.What factors might affect the magnitude of the temperature change?
5Specific heat capacity The amount of energy Q required to change the temperature of a given material is proportional to the mass m of the material and to the temperature change ΔT, shown by the simplistic expression:Q = mc ΔTwhere c is the characteristic of the material called its specific heat capacity
6Specific heat capacity A high specific heat capacity means that more energy is required to achieve the same temperature change, i.e. it is more “difficult” to raise the temperature of that material.If a material is a good heat conductor (e.g. metals) would you expect it to have a high or low specific heat capacity?
7Specific heat capacity Specific heat capacities of specific substancesSubstanceSpecific heat capacity, c / Jkg-1°C-1aluminum900copper390iron or steel450lead130wood1700water (ice)2100water (liquid)4186water (steam)2010human body (average)3470
8Specific heat capacity Q / Jm / kgc / Jkg-1C-1ΔT / °C or °K?increasedconstant
9Specific heat capacity How much heat input is needed to raise the temperature of an empty 20-kg vat made of iron from 10C to 90C?What if the vat is filled with 20 kg of water?
11Specific heat capacity You accidentally let an empty iron frying pan get very hot on the stove (approx. 200C). What happens when you dunk it into a few inches of cool water in the bottom of the sink? Will the final temperature be midway between the initial temperatures of the water and pan? Will the water start boiling? (Assume the mass of the water is roughly the same as the mass of the pan.)
12CalorimetryIn discussing heat and thermodynamics, we shall often refer to systems.What is the difference between open, closed, and isolated systems?
13Calorimetry Open system Closed system Isolated system Mass and energy may leave and enterClosed systemEnergy may leave and enter but mass may notIsolated systemNeither mass nor energy may leave or enter
14CalorimetryWe will often make the assumption that the systems we are dealing with are isolated.Why is this necessary?
15energy out of one part = energy into another part CalorimetryIn an isolated system, heat lost by one part of the system is equal to the heat gained by another part:heat lost = heat gainedorenergy out of one part = energy into another part
16CalorimetryIf 200 cm3 of tea at 95C is poured into a 150-g glass cup initially at 25C, what will be the common final temperature T of the tea and cup when thermal equilibrium is reached, assuming no heat flows to the surroundings?
17CalorimetryT = 86C Would this be the case in the “real world”?
18CalorimetryThe exchange of energy (as shown in the previous example) is the basis for the technique known as calorimetry.Calorimetry is the quantitative measurement of heat exchange.A calorimeter is used.
20CalorimetryAn engineer wishes to determine the specific heat of a new metal alloy. A kg sample of the alloy is heated to 540C. It is then quickly placed in 400 g of water at 10.0C, which is contained in a 200-g aluminum calorimeter cup. The final temperature of the system is 30.5C. Calculate the specific heat of the alloy.
22where the two substances share a final temperature CalorimetryIn order to determine the specific heat of a particular substance, the following expression is used:Qlost = Qgainedm1c1ΔT1 = m2c2 ΔT2where the two substances share a final temperatureThus, all other quantities except one must be measured or known.
23Phase changeRecall that matter most commonly exists in three states: solid, liquid, and gas.What are the differences between these three states (or phases) in terms of molecular structure and motion?
24Phase change Shape Volume Particle motion solid liquid gas Comparison of the three common phases of matter (on Earth)ShapeVolumeParticle motionsolidliquidgas
25same as liquid but quicker Phase changeComparison of the three common phases of matter (on Earth)ShapeVolumeParticle motionsoliddefinitevibrationalliquidindefiniterotationaltranslationalgassame as liquid but quicker
26Phase changeWhen a material changes phase from solid to liquid or liquid to gas, a certain amount of energy is involved in this change of phase.
27Phase changeTemperature as a function of heat added to 10.0 g of ice
28Phase changeThe heat required to change a substance from solid to liquid is called latent heat of fusion.The heat required to change a substance from liquid to gas is called the latent heat of vaporization.Values for latent heats will vary depending on the substance.
29Phase change Latent heats Substance Heat of fusion / kJkg-1 Heat of vaporization /oxygen14210ethyl alcohol104850water3332260iron2896340
30Phase changeWhat factors might affect the amount of energy needed to change the phase of a substance?
31where m is the mass of the substance and L is the latent heat Phase changeThe heat involved in a change of phase Q depends not only on the latent heat but also on the total mass of the substance, i.e.Q = mLwhere m is the mass of the substance and L is the latent heat
32Phase changeHow much energy does a freezer have to remove from 1.5 kg of water at 20C to make ice at –12C?
34Phase changeAt a reception, a 0.50-kg chunk of ice at –10C is placed in 3.0 kg of tea at 20C. At what temperature and in what phase will the final mixture be? The tea can be considered as water. Ignore any heat flow to the surroundings, including the container.
36Phase changeThe specific heat of liquid mercury is 140 Jkg-1C-1. When 1.0 kg of solid mercury at its melting point of –39C is placed in a 0.50-kg aluminum calorimeter filled with 1.2 kg of water at 20.0C, the final temperature of the combination is found to be 16.5C. What is the heat of fusion of mercury in Jkg-1?
38Objectives Define specific heat capacity. Solve problems involving specific heat capacities.Explain the difference between solid, liquid, and gaseous phases.Explain in terms of molecular behavior why temperature does not change during a phase change.Define latent heat.Solve problems involving latent heats.
39Measuring specific heat Data collectionmass of metalinitial temperature of metalmass of calorimetermass of calorimeter + waterinitial temperature of waterfinal temperature
40Measuring specific heat Data processingInclude propagation of uncertaintymass of waterΔT of waterΔT of metal
41Measuring specific heat Data processingInclude propagation of uncertaintyQ = mcΔTQ (lost) = Q (gained)mass of waterΔT of waterΔT of metal
42Measuring specific heat HomeworkWrite a conclusion and evaluation of the lab activityDesign a homemade calorimeter using the materials available. Try to minimize the amount of energy lost to the surroundings.You will use this calorimeter for the next lab activity. The calorimeter with the smallest percent discrepancy gets bonus points.
43Measuring latent heat of fusion Data collectionmass of cup 1mass of cup 1 + watermass of cup 2mass of cup 2 + iceinitial temperature of iceinitial temperature of waterfinal temperature
44Measuring latent heat of fusion Data processingmass of waterΔT of watermass of iceΔT of ice
45Measuring latent heat of fusion HomeworkComplete your data processing.Make sure to include a sample calculation that shows the propagation of uncertainty.Write a conclusion for your data, is the known value for the latent heat of fusion of water within your range of uncertainty?