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 takePROPANE 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 componentsProteins 4 cal/gCarbohydrates 4 cal/gFats 9 cal/g

It’s Experiment Time!

VS

Comparing itCHEETOS

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

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 CalorimeterOften 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 followedSix Steps of Preparation

1. What do we need to find?

2. What numbers do we have?

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?

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?

Question 2: On your ownOn 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?

HomeworkFinish 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