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Q = MCΔT – Specific Heat & CALORIMETRY Burnin’ Up.

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Presentation on theme: "Q = MCΔT – Specific Heat & CALORIMETRY Burnin’ Up."— Presentation transcript:

1 Q = MCΔT – Specific Heat & CALORIMETRY Burnin’ Up

2 What is heat? Thermal energy (kinetic) produced by the movement of molecules

3 Why might we want to measure heat?

4 We’re going camping… I can only take 1L of gas. Should I take PROPANE GAS? or BUTANE GAS? How might I decide?

5 How about another example…

6 How many calories are in our food?

7 What are ‘calories’ in food? How much ‘energy’ you will gain if you eat it How much heat will be produced if we burn it

8 How do we determine the caloric content of food? BURN IT!!! Nowadays they use more sophisticated methods to determine the components Proteins 4 cal/g Carbohydrates 4 cal/g Fats 9 cal/g

9 It’s Experiment Time! VS

10 Comparing it CHEETOS 550cal for 95 grams = 5.78cal/gram x 4.184KJ/cal = 24.18 KJ/gram CHIPS 390cal for 75 grams = 5.2cal/gram x 4.184KJ/cal =21.76kJ/gram

11 We’ve been talking about Q=MC(delta)T What is Calorimetry? the technological process of measuring energy changes in a chemical system What is a Calorimeter? A device used to measure the energy change of a chemical system Used to insulate the reaction against energy/product loss

12 Examples of Calorimeters

13 Bomb Calorimeter Often used for combustion reactions (not necessarily for ‘bombs’!)

14 Calorimetry Questions

15 Question 1: Together It takes 41.8J to heat a 0.01869kg chunk of gold from 10 o C to 27 o C. Calculate the specific heat capacity of gold.

16 Steps we followed Six Steps of Preparation  What do we need to find?  What numbers do we have?  What ‘hidden numbers’ do we have?  What equation(s) can we use?  Do we need to rearrange the equation?  Do we need to convert any units? Four Steps of Action 7. Sub in the numbers 8. Do the math – WITH UNITS! -- WITH SIGNS! (+/-) 9. Round the answer to the appropriate significant digits 10. Check your answer: Does it make sense? Does it answer the question that was being asked?

17 Question 2: On your own On a mountaineering expedition, a climber heats water from 0 o C to 50 o C. Calculate the mass of water that could be warmed by the addition of 8.00kJ of heat.

18 Let’s take it one step further I took a 0.400kg block of Aluminum, and heated it on a hot plate to 212 o C. I then transferred it to 0.800L of water at 23.0 o C. The final temperature of the system was 41.35 o C. What is the specific heat capacity of aluminum?

19

20 Homework Finish pre-lab for NEXT CLASS (Friday) No pre-lab = no lab Calorimetry worksheet is due on TUESDAY Look over ‘cheat sheet’ – it may help you understand the worksheet


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