Burn, baby, burn: An introduction to energy Unit 2 Energetics/Thermochemistry: Chapter 5 in your IB textbook!

BUT WHY??? Black board demo with ice cubes DEMO to get us started!

In this unit…and more! Why do explosions happen? Why are some reactions cold and some hot? Why is Rome’s weather so temperate? Why does the floor feel SO cold in the morning? In this unit…and more!

Definition: The ability to do work or produce heat What is Energy?

Video on Heat versus Temperature Watch this Video on Heat versus Temperature

Heat = total KINETIC ENERGY transferred from one object to another NOT a substance. Just energy moving. Temperature = how much ENERGY an object’s molecules have on average How fast are the particles moving on average? What is heat?

Laws of Thermodynamics First law: Energy is conserved in a system Heat in = Heat out Second law: Energy wants to disperse (come to thermal equilibrium) Heat won’t “bunch” up in one place – it always spreads by molecule movement! These concepts relate to gases quite a bit! HEAT FLOWS Laws of Thermodynamics

WRONG! Heat flows HOT  COLD You’ll let the cold in!

Heat Flow Video Watch this: Energy and heat flow Stop at 2:40 min – we’ll go through the rest next week Heat Flow Video

How is heat transferred?

Thermal equilibrium: Heat flows until the temperatures in each object are the same When does the heat stop?

q in = q out 1st law: Energy is conserved in a system If something cold is mixed with something warm, thermal equilibrium is reached. The energy (heat) given from the warm object is equal to the energy taken by the cold object! q in = q out

Activities with alcohol Activities: In your notes! 1) Place a few drops of ethanol on your hand – explain what you feel and try to explain it! 2) Take a thermometer with cotton on the end and add a few drops of ethanol to the cotton. Observe and explain what you see! Activities with alcohol

Explain the activities Evaporation – what did YOU feel? Why? Temperature – why did the temperature go DOWN? 1) Ethanol taking heat FROM your hot hand and using that energy to evaporate – feels cold to us! 2) As ethanol and the metal from the thermometer meet, even though they are at the same temperature, the most energetic molecules in the ethanol escape into vapour phase, leaving only the colder ones (Think Maxwell-Boltzmann distribution!). So then, the leftover ethanol molecules are (on average) colder than the metal thermometer, so the heat is stolen and we see that as a decrease in temperature reading on the thermometer. Explain the activities

Joule = (SI unit of energy) work to move an object 1 meter with 1 Newton of force Work energy is related to heat energy Think friction! calorie = energy needed to raise 1 gram of water 1 degree Celsius Relationship between: 1 calorie = 4.184 Joules James Prescott Joule Units of Energy

If you have 4.0 grams of water, how many calories are required to raise the temperature 2.0 degrees Celsius? How many Joules is that? 8 calories! Practice it!

q = mcΔT q = total heat transferred to or from (J) m = mass of the substance in grams c = heat capacity (J/g°C) How many Joules does it take to raise 1 gram of the substance 1 degree Celsius? c of water = 4.184 J/g°C ΔT = absolute value of change in temperature in the system (K or °C) Note – we can’t measure total HEAT, we can only measure heat transfer through calorimetry (transferring to water) q = mcΔT

Calorimetry! Standard Calorimeter Bomb Calorimeter Coffee Cup Calorimeter Calorimetry!

Now it’s time to prepare for Lab 9 on Wednesday in class! Unknown Heat Capacity Lab #9: find the heat capacity of the metal washer

q lost by metal = q gained by water How to find the unknown c: Calculate the specific heat capacity (c) for the metal using the ΔT and mass of the metal and the ΔT, of water, and mass of the water Only one unknown variable! (Cmetal) q lost by metal = q gained by water m c ΔT = m c ΔT

Pre-lab (and lab book set up) ready for Lab 9 next class Wednesday Including pre-lab question Read and notes: Chapter 5, pgs 165- 174 (HL 210-220) Review about exo and endothermic reactions Heat flow Heat capacity Example calculations (helpful for Lab 9) HOMEWORK DAY 1

Watch this video on heat capacity, specific heat, and calorimetry so you understand Lab 9! He calls heat capacity s instead of c, but it’s the same equation! Do the practice problem at the end in your notes, too! Calorimetry Video

Demos – every material is different! Every material (rock, bone, brass, dirt, air) has its own ability to store heat! Called heat capacity Specific heat capacity = how much heat (in Joules) does it take to raise 1 gram of that substance 1 degree Celcius? Ice cube demo, washers – how quickly do they heat up? What about something else? Hold hands, etc? Demos – every material is different!