Do Now (2/16/12) (7-8 min): Convert the following temperatures: 1. 39˚F=____˚C 2. 10˚C=____K ˚C=____˚F K=____˚C K=____˚C

Do Now (2/16/12) (7-8 min): Convert the following temperatures: K =____˚C 2. 10˚C=____K 3. 0 ˚C=____˚F Identify the types of heat transfer in each example: 4. Sitting in the sun 5. Heating up a cup of coffee 6. Heating a pan on an electric stove

Heat Transfer 2/18/11

Heat The energy that is transferred between objects

Brainstorm (2 min): Is heat transferred when the temperature of an object changes? Brainstorm, and write an answer in your notes. Discuss with your partner once you’ve finished. *thinking point – what does “temperature” mean? YES!!! Heat transfer means a change in energy, which means a change in temperature!!!

Heat Transfer Due to Temperature Change: Heat lost or gained (Q) Q=heat (measured in J) m=mass C=specific heat ∆T=T f –T i =change in temperature (˚C/K)

Specific Heat ( C ) the amount of heat per unit mass required to raise the temperature by one degree Celsius; it is unique to and constant to each materialheattemperature Measured in:

Specific Heat (C) Specific heat can be looked up in tables based on the MATERIAL (ex. Water = 4180 J/kgK)

Example: What is the heat gained when a 1.3 kg sample of water is heated from 10˚C to 30˚C. If the specific heat of water is 4180 J/kgC, how much heat did the water gain or lose? Step 1: List knowns/unknowns m=1.3 kg T i = 10˚C T f = 30˚C C=4180 Q=? Step 2: Find an appropriate equation Step 3: Plug in and solve

Solving for final and initial temperatures *reminder: ΔT=T f -T i When ask to solve for T f or T i, replace ΔT with T f -T i Example: Q=mC ΔT  Q=mC(T f -T i )

Heat If heat is absorbed, Q is + If heat is released, Q is -

*note The heat transfer we have discussed today is for ONE object at a time… tomorrow we will discuss heat transfer between TWO objects.

Practice 2/16/12: Please use the rest of class to work on the paper “Heat Transfer B.” It is due on Tuesday, 2/21/12 *for #’s 1 and 2 on your paper, assume C=4180. Thanks! Specific heats: Mercury: 114 J/kgC Specific heats are found on p. 279 of your textbook

Do Now (2/17/12): A 20 kg sample of water is cooled from 90˚C to 40˚C. If the specific heat of water is 4180 J/kgC, how much heat did the water gain or lose?

Heat Transfer Heat flows from one object to another until they are in thermal equilibrium. Thermal equilibrium: all objects in a system have the same temperature

Calorimetry: science of measuring the heat of physical changes

Heat Transfer Heat is thermal energy (cannot be created or destroyed):

Solving For Final Temperature

Solving for Final Temperature A 0.4 kg sample of water is at 90 ˚ C is mixed with a 0.7 kg sample of methanol (specific heat 2450 J/kgC) initially at 20 ˚ C. Assuming no heat loss to their surroundings what is the final temperature of the mixture?

Mouse traps “Victor” brand (if you would like to buy your own). You may sign up for me to buy yours – they are $1 each.

Practice (2/17/12): Please use the rest of class to work on the paper “Heat Transfer.” It is due on Tuesday!!! Specific heats can be found on p. 279 of your textbook.

Do Now (2/21/12): A 2 kg sample of water (specific heat 4180 J/kgC) is at 75 ˚ C is mixed with a 3 kg sample of methanol (specific heat 2450 J/kgC) initially at 25 ˚ C. 1. List your variables. 2. Assuming no heat loss to their surroundings what is the final temperature of the mixture?

Pass in: Pass in homework (unless you were on the field trip Thursday); then please take out the notes you have taken so far in this unit. *note – you will have a short quiz tomorrow on thermal energy

Do Now: A physicist plans to change 100 grams (0.100 kg) of ice at –10.0 o C into 100 g of water at 0 o C. What is the heat required to raise the ice to its melting point? The specific heat of ice is 2060 J/kgC

Calorimetry A 12.9 gram sample of an unknown metal at 26.5°C is placed in a Styrofoam cup containing 50.0 grams of water at 88.6°C. The water cools down and the metal warms up until thermal equilibrium is achieved at 87.1°C. Assuming all the heat lost by the water is gained by the metal and that the cup is perfectly insulated, determine the specific heat capacity of the unknown metal. The specific heat capacity of water is 4180 J/kg°C

Do Now: A 30 g sample of an unknown metal at 28°C is placed in a Styrofoam cup containing 50 g of water at 89°C. The water cools down and the metal warms up until thermal equilibrium is achieved at 87°C. Assuming all the heat lost by the water is gained by the metal and that the cup is perfectly insulated, determine the specific heat capacity of the unknown metal. The specific heat capacity of water is 4180 J/kg°C

Do Now: A 0.4 kg sample of water (specific heat 4180 J/kgC) is at 90 ˚ C is mixed with a 0.7 kg sample of methanol (specific heat 2450 J/kgC) initially at 20 ˚ C. Assuming no heat loss to their surroundings what is the final temperature of the mixture?

Calorimetry Calorimetry : science of measuring the heat of physical changes Calorimeter – a device used for measuring specific heat capacity