SE 402 1 Heat Energy, Part a

Module 2 – Heat Energy

Objectives5.2 Calculate heat energy, using a

mathematical relationship.

Heat Energy:

Heat (thermal) energy is simply a type of energy Ex. heat from a stove Ex. heat from a light bulb

Heat energy can be transferred from one object to another Ex. from a hot coffee cup to your

cold hands

What is heat energy?

Q = mC∆THeat

EnergyJoules (J)

mass grams (g)

Change in Temperature

DegreesoC

Specific Heat

Capacity(J/g•oC)

Specific Capacity (c) specific heat capacity (c) - the amount of

energy absorbed by a substance or object.

It is a characteristic property.Substances Joules/(g• 0C)Copper 0.383

Iron 0.452

Aluminum 0.896

Antifreeze 2.2Methanol 2.547

Water 4.19

Every substance has their own specific heat capacity that does not change. However, water is most commonly used in exam

questions.

A pot with 500g of water is placed on a stove. The temperature of the water increased from 20oC to 100oC. How much heat was absorbed by the water?

m = 500g

Ti = 20oC

Tf = 100oC

c = 4.19 J/goC

Q = mc∆T

Q = (500)(4.19)(100-20)

Q = 167,600 JRecall: The “c” of water

is 4.19 J/goC

A 250g glass of cold ice water is placed outside in the sun. The temperature of the water rises from 5oC to 25oC. How much heat was absorbed by the water?

m = 250g

Ti = 5oC

Tf = 25oC

c = 4.19 J/goC

Q = mc∆T

Q = (250)(4.19)(25-5)

Q = 20,950 J

A 20g iron frying pan is heated from 21oC to 85oC. If the specific heat capacity of iron is 0.45 J/goC, how much heat was absorbed by the firing pan?

m = 20g

Ti = 21oC

Tf = 85oC

c = 0.45 J/goC

Q = mc∆T

Q = (20)(0.45)(85-21)

Q = 576 J

A 250mL of water at 30oC is heated until it boils at 100oC. How much heat was absorbed by the water?m = 250 g

Ti = 30oC

Tf = 100oC

c = 4.19 J/goC

Q = mc∆TQ = (250)(4.19)(100-30)

Q = 73,325 J

To go from volume to mass: times volume of water by the

density of water. So,1g/mL x 250 mL = 250 g

Note for water: 1mL = 1g

A 1500mL of water at 5oC is heated until it reaches 37oC. How much heat was absorbed by the water?

m = 1500 g

Ti = 5oC

Tf = 37oC

c = 4.19 J/goC

Q = mc∆T

Q = (1500)(4.19)(37-5)

Q = 201,120J

Note for water: 1mL = 1g

20,112J of energy is used to heat water from 2oC to 50oC. How many grams of water was heated?

m = ? gTi = 2oC

Tf = 50oC

c = 4.19 J/goC

Q = 20, 112J

Q = mc∆T

20,112 = (?)(4.19)(50-2)

m = 100 g

20,112 = (?)(201.12)

20,112 = (?)(201.12) 201.12 201.12

360J of energy is used to heat a 20g piece of iron from 20oC to 60oC. What is the heat capacity of iron?

m = 20 g

Ti = 20oC

Tf = 60oC

Q = 360J

c = ? J/goC

Q = mc∆T

360 = (20)(?)(60-20)

c = 0.45 J/goC

360 = (800)(?)

360 = (800)(?) 800 800

A calorimeter was used to heat 300ml of water to 70oC. If the thermal (heat) energy was equal to 62850 J, what was the initial temperature of the water before being heated?

m = 300 g (remember 1 g = 1ml)c = 4.19 Joules/(g• 0C)Ti= ? TF= 70 0CQ = 62850 J

Q = mc∆T62850 = 300 x 4.19(70 - Ti)62850 = 1257(70 - Ti)62850 = 87990 – 1257Ti-25140 = - 1257Ti

20 0C= Ti

TrickyQuestion

A calorimeter was used to heat 400ml of water to 40oC. If the thermal (heat) energy was equal to 5.4 kJ, what was the initial temperature of the water before being heated?

m = 400 g (remember 1 g = 1ml)c = 4.19 Joules/(g• 0C)

Ti= ?

TF= 40 0CQ = 5400 (5.4kJ = 5400 J)

Q = mc∆T5400 = 400 x 4.19(40 - Ti)5400 = 1676(40 - Ti)5400 = 67040 – 1676Ti-61640 = - 1676Ti

36.8= Ti

TrickyQuestion

Q = mc∆T (J) (g)(J/g•oC)

o Heat capacity of water is 4.19 J/g•oC

o 1 g of water = 1 ml of water

o Q is always in Joule (j) not kJ!

Tf –Ti

(oC)

Activities

Worksheet # 17

First Law of Thermodynamics

This law states that “in an isolated system energy remains constant”.

This means that energy can be transformed (neither created nor destroyed).

Example: When you eat a candy bar the bar is transformed into energy within your body.

Different Types of Energy

Thermal

Light

Electrical


Magnetic

Nuclear

Kinetic

Potential

Chemical

Sound

Aeolian


Tidal

Geothermal

Hydro

Solar


References

Student Study Guide Physical Science 416 – MEQ

Science Quest, Grenier, Daigle & Rheaune, 1998 Editions Cheneliere

Animation Factory Google Images

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