Chapter 11

• Thermodynamics is the study of heat changes in chemical processes.– When you light a campfire, a lot of heat is

given off. This is an exothermic process.– When you hold an ice cube, your hand gets

cold & the ice melts. Heat is absorbed by the ice. This is an endothermic process.

• There are many more examples of both exothermic processes and endothermic processes, and we will examine some later. Now, we need to talk about heat.

What is heat? (Click on the correct answer.)

Matter Energy

You answered correctly!

Heat is not matter because it does not have mass or volume.

Heat is a form of energy.

More About Heat

Remember, matter must have both a volume and a mass.

Heat does not have a volume or a mass.

Go Back and Try Again

• Heat is energy that is transferred from one object to another because of a temperature difference.

• Heat is represented as the letter Q – be sure to remember this later – we will use Q in the thermochemistry formulas.

• Heat (Q) can be in joules or calories.

• Heat itself cannot be detected – instead, we detect the temperature changes in objects caused by the addition or release of heat.

• Heat always flows from an object of higher temperature to an object of lower temperature.

• Which of the following is an example of an exothermic process?

A

B

Fireworks exploding on July 4th.

Chemicals are mixed in a test tube, and the tube gets very cold.

You are correct!

Fireworks exploding give off a lot of heat.

That means it is an exothermic process.

Next Topic

An exothermic process would make a test tube hot.

An endothermic process would make a test tube cold.

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• Heat is a form of energy no matter if its being absorbed or released

What is ENERGY?

• Energy is the capacity for doing work or supplying heat. For example, gasoline has a lot of stored chemical energy – when it is burned, it makes your car go.

• Energy is weightless, odorless and tasteless. In other words, it has no mass or volume. Heat is just one example of energy.

• When you eat food, you get the energy stored in the food to do the things you do throughout the day – sleep, ride your bike, watch TV or do your homework.

• Some foods have more stored energy than others, but how can we tell which ones will give us more energy?

• You can look at the nutrition label on the package to find out how much energy the food can give you

• The unit of energy you will see on food packages in America is called the Calorie.

• Calories are just one unit of energy

• When talking about the energy in food, we use Calories

• Calories (with a capital C) really means 1000 calories or 1 kilocalorie

• The exact definition of a calorie (lower case c) is:

– The amount of energy (or heat) needed to raise the temperature of 1g pure water by 1oC

• Of course, in our bodies, we use the calories in food to do more than heat water

If the nutrition label of your favorite food says it has 120 Calories per serving, how many calories does it have per

serving?

A B12,000 calories 120,000 calories

Good Job!

If there are 120 Calories, there are 120,000 calories per serving

Next Topic

You need to multiply the Calories by 1000 to get calories.

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• Another unit of energy is the Joule

• There are 4.184 Joules in 1 calorie

• Joules are the SI unit of heat and energy

• One Joule will raise the temperature of 1g of pure water 0.2390oC

• We can use Joules when we are working with formulas in Thermochemistry

• You must be careful, though, because calories can also be used

• As with everything else in chemistry: Mind Your Units!

Next Topic

• We have one last concept to cover before we move on to Formulas

• It is possibly the most important concept in this chapter – Specific Heat

• You encounter the effects of specific heat almost every day

• The specific heat of a substance is the quantity of heat, in calories or joules, required to raise the temperature of 1g of that substance 1oC

• Pure water (H2O) has a specific heat of 1 calorie per gram-degree Celsius (cal / goC)

What does that mean?

• That means if you have 1g of water at 25oC, you will need to add just 1 calorie to raise the temperature to 26oC.

• If you have 10g of water at 25oC, you will need to add 10 calories to raise the temperature to 26oC.

If you have 200g of pure water, how many calories would you need to add to change the temperature from 25oC to 26oC?

A 200 calories B 100 calories

Good Job! You answered correctly!

It would require 200 calories to raise the temperature of 200g of pure water from 25oC

to 26oC!

It would also take 200 calories to raise the temperature from 26oC to 27oC, one calorie

for each gram.

More Information

You need 1 calorie for each gram of water when you want to raise the temperature by

only 1oC.

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• Each pure substance has a unique specific heat

• Water’s specific heat is very high compared with the specific heat of other substances

• Iron, for example, has a specific heat of 0.11 cal / goC

• An iron rock with a mass of 300g at 25oC, would require 33 calories to raise the temperature to 26oC

• 300g of pure water at 25oC would require 300 calories to raise the temperature to 26oC

• Because metals have low specific heats, a metal pot will be very hot even though the water inside is still lukewarm.

• If the stove is turned off, the same metal pot will be cool to the touch before the water is.

Use Chapter 11 of your Chemistry book to find the specific heat of the following substances in cal / gcal / gooCC:

Aluminum Glass Ice Chloroform

Email me with your answers.

Which phrase best describes the concept of specific heat?

AWater has a high specific heat, so it takes less heat added to make water hot

B

Water has a high specific heat, so it takes more

heat added to make water hot

You need to add a lot of heat to water in order for its temperature to change.

Go on to Formulas

Remember, the metal pot will heat up before the water will. You need to continue heating the water for it to get hot.

Go Back and Try Again

• The formula for specific heat is

C = Q / m x C = Q / m x TTCC = specific heat

QQ = calories or joules

mm = mass in g

TT = temperature change in oC

Let’s try a sample problem:

You find a rock with a mass of 95g. You would like to know its specific heat. You find, through experimentation, that it takes 200cal to raise the temperature of the rock from 25oC to 30oC. What is its specific heat?

Lets fill in the variables:

C = 200cal / 95g x 5oC

C = 200cal / 475goC

C = 0.42cal / goC = The specific heat of the rock

Try these next few problems on your own, in a Word Word DocumentDocument. Show your work and watch the units! Print it

out and hand it in.

1. What is the specific heat of a piece of unknown metal if it takes 85cal

to raise the temperature of 148g 10oC? What metal might this be?

2. The temperature of a piece of copper with a mass of 95.4g increases

from 25oC to 48oC after absorbing 849J. What is the specific heat?

3. A piece of stainless steel weighing 1.55g absorbs 33.7cal and its

temperature is increased by 178oC. What is the specific heat of

stainless steel?

Next Formula

• The formula for heat is:

Q = C x m x Q = C x m x TT

Remember, Q can be in calories or joules

Let’s try a sample problem:

You have to heat 565g of pure water from

25oC to 35oC. You know the specific heat of

water is 4.18 J/goC. How many joules of heat

do you need to add to the water?

Q = 4.18J/goC x 565g x 10oC

Q = 4.18J/goC x 5650goC

Q = 23,617J (goC have canceled out) = the amount of heat needed

• The formula for mass is:

M = Q / C x M = Q / C x TT

• The formula for change in temperature is:

T = Q / C x mT = Q / C x m

You have a 56g chunk of iron metal (C=0.11cal/goC). The chunk absorbs 450cal when you heat it. What was the temperature change of the metal?

A 73.0oC B 0.884oC

That’s correct!

The formula would look like this:

450cal / (.11cal/goC x 56g).

Next Question

You need to use the formula for T.

450cal = Q, 56g = m & 0.11cal/goC = C.

Go Back and Try Again

You add 752J to a sample of water. The temperature change is only 3oC. What mass of water do you have? Remember, the specific heat of water is 4.18J/goC.

A B 60.0g H2O540g H2O

That’s right! The formula would be:

752J / (4.18J/goC x 3oC).

Homework

In this problem, you need to use the formula for mass.

C = 4.18J/goC, T = 3oC & Q = 752J

Go Back and Try Again

For homework, open Worksheet Worksheet

11.1 11.1 and complete the problems.

Show your work and watch the

units! Print it out and hand it in

when you are finished.

H O M E W O R K

• The first thing to note about lava is that not all lava is the same, in fact, lava from one volcano will be different from the lava of another

• All lava can be grouped into four main types:– Lava with a lot of iron & magnesium– Lava with a lot of aluminum & silicon– Lava with iron, magnesium, aluminum & silicon– Lava with gases such as carbon dioxide

• The temperature of lava will vary, but Rhyolite (rich in silicon & aluminum) is about 1250oC

• Rhyolite is over 60% SiO2, but we will assume it is 100% for this activity

• We will assume the specific heat to be an average of 0.7485J/goC, or 0.179cal/goC

• We will assume that, in one day, a volcano can erupt 1.24x1012g of Rhyolite lava

• Eventually, lava will cool to the temperature of the air – we will assume this to be room temperature - 25oC

• The temperature change is from 1250oC to 25oC, or 1225oC

• We know the specific heat, mass and temperature change of the lava, so we can now figure out the amount of heat lost when the lava cools

• Remember: Q = C x m x Q = C x m x TT

Using the values given previously, calculate the amount of heat given off by the cooling lava in calories.

A B C2.72x1014cal5.65x109cal 1.14x1015cal

That’s the right answer!

Q = 0.179cal/goC x 1.24x1012g x 1225oC

Q = 2.72x1014 cal

The End!The End!

Extra Extra Credit!Credit!

We are looking for Q in calories, so be careful of the units used.

Make sure you are using the correct equation, Q = C x m x Q = C x m x TT.

Go Back and Try Again

Calorie – the quantity of heat that raises the temperature of 1g of pure water by 1oC

Endothermic Process – a heat absorbing process

Energy – the capacity to do work, could be chemical energy, thermal energy, electrical energy etc.

Enthalpy – heat content of a system at constant pressure

Exothermic Process – a heat releasing process

Glossary Next Page

Heat – energy that is transferred from one object to another due to a temperature differenceHeat Capacity – the quantity of heat required to change the temperature of an object by exactly 1oCJoule – the SI unit of energy, 4.184J = 1 calorie

Specific Heat – the quantity of heat, in calories or joules, required to raise the temperature of 1g of a substance 1oC

Thermochemistry – the study of heat changes in chemical reactions

Glossary Previous Page

• Lets assume there is a volcano that is next to a lake. The lake is filled with fresh water & has a volume of 2.0x1018ml H2O. Assume the specific heat of the lava is 0.179cal/goC, the mass of the lava spilled into the lake is 1.24x1012g, and the temperature of the lava goes from 1250oC to 10oC. What is the temperature change of the lake, assuming the specific heat of the water is 1.0cal/goC & the density of the water is 1g/ml. Does this surprise you? Why or why not?

Extra Credit Problem

Answer on a piece of paper & hand in!