Transcript Q = MC*T * Specific Heat - OISE-IS-Chemistry-2011-2012

Q = MCΔT – Specific
Heat & CALORIMETRY
Burnin’ Up
What is heat?
 Thermal energy (kinetic) produced by the
movement of molecules
Why might we want to
measure heat?
We’re going camping…
 I can only take 1L of gas.
Should I take
 PROPANE GAS?
 or BUTANE GAS?
 How might I decide?
How about another example…
How many calories are
in our food?
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
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
It’s Experiment Time!
VS
Comparing it
CHEETOS
CHIPS
 550cal for 95 grams
 390cal for 75 grams
 = 5.78cal/gram
 = 5.2cal/gram
 x 4.184KJ/cal
 x 4.184KJ/cal
 = 24.18 KJ/gram
 =21.76kJ/gram
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
Examples of Calorimeters
Bomb Calorimeter
 Often used for combustion reactions
(not necessarily for ‘bombs’!)
Calorimetry Questions
Question 1: Together
It takes 41.8J to heat a 0.01869kg
chunk of gold from 10oC to 27oC.
Calculate the specific heat capacity of
gold.
Steps we followed
Six Steps of Preparation
Four Steps of Action
1. What do we need to find?
7. Sub in the numbers
2. What numbers do we have?
8. Do the math
3. What ‘hidden numbers’ do
we have?
4. What equation(s) can we
use?
5. Do we need to rearrange
the equation?
6. Do we need to convert any
units?
– 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?
Question 2: On your own
On a mountaineering expedition, a climber
heats water from 0oC to 50oC.
Calculate the mass of water that could be
warmed by the addition of 8.00kJ of heat.
Let’s take it one step further
I took a 0.400kg block of Aluminum, and
heated it on a hot plate to 212oC.
I then transferred it to 0.800L of water at
23.0oC. The final temperature of the system
was 41.35oC.
What is the specific heat capacity of
aluminum?
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