Heat and Heat Measurements

7/25/2019 Heat and Heat Measurements

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Heat and HeatMeasurements


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Defnition oHeat

Heat a fundamental form of energy

that can be transformed from one formto another. It can also be transferredfrom one point to another by the virtue

of the motion of the molecules broughtabout by the dierence intemperature.

Unit mass a scalar quantity ofmagnitude:

Cgs 1 gm, mks 1 kg, fps 1 slug

nits of !eat Conversion

" "


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+ote:

1 calorie the amount of heat needed toraise the temperature of 1 gm ofater by 1C -.

1 kilocalorie the amount of heat needed toraise the temperature of 1 kg ofater by 1C -.

1 '( 'ritish (hermal nit/ the amount of

heat needed to raise thetemperature of 1 slug of ater by10-.


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2 Common Eects o Heat

1. Change in temperature

). Change in hase

Change in (emperaturem

m

3here:m " mass of the bodyC " speci4c heat5t " change intemperature


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Heat Quantity (Q) the total amount

of heat involved to change thetemperature of the total mass ofthe substance 6o a change in

phase.Specifc Heat (c) the amount of

heat needed to raise thetemperature of a unit mass of asubstance by 1-.


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Units CGS MKS !S

C Ca"#$%c& Kca"#$%c& 'U#s"u$%&

Units and a"ues o SpecifcHeat* C


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C+an$e in !+ase

0i7ed oints points at hich asubstance ill have a changeits phase ithout a change intemperature.

ree,in$ !oint#Me"tin$ !oint

ice

or -2&

.ater

or -2&

(/) +eat $ained or a0sor0ed (%) +eat "ost orre"eased


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'oi"in$ !oint#Steam !oint

steam

(/) heat gained or absorbed (%) heat lost or

released


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Heat Quantity (Q) the total amount ofheat involved to change the phase

of the entire mass of the substance6o a change in temperature.

1atent Heat (1) the amount of heat

needed to change the phase of aunit mass of a substance hen nochange in temperature takes place.

1atent Heat o usion (1) theamount of heat needed to change aunit mass of ice to ater or vice8versaat free9ing point or melting point.


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1atent Heat o apori,ation (1) the amount of heat needed to

change a unit mass of ater tosteam or vice8versa at boiling pointor steam point.

a"ueso 1

c$s m3s ps

$

cal6g

$

kcal6kg

1##

'(6slug*#cal6g

*#kcal6kg

;


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Calorimetry the measurement of heatquantities using a calorimeter

=t thermal equilibrium tmi7/, all bodiesstirrer, calorimeter, !)> and metal/ ill have

the same temperature.


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!rincip"e o ca"orimetry

!otter bodies ill give o heat Colder bodies ill absorb heat

'y conservation of heat energyHeat "ost 0y+otter 0ody 4 +eat

$ained 0y co"der 0odies


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'y conservation of heat energy

5

wcsm QQQQ ++=

tmcQ =

wwwcccsssmmm tcmtcmtcmtcm ++=

mmixm ttt = wmixwcs ttttt ===

( ) ( )wmixwwccssmixmmm

ttcmcmcmttcm ++= )(


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?=@AB >'AB@?

1.How much heat is needed to change 10 g of ice at -20 oC to

steam at 110oC assuming no heat is lost due to the

surrounding? Ans. QT= 7350 cal

2. It is found out that 100 kcal of heat is just sufficient in

changing a certain amount of ice at -20oC to steam at 130oC.

etermine the mass of the ice. Ans. m = 0.13 kg

3. 100 g of ice at 0oC are dro!!ed into 3"1.# gm of water at30oC contained in a 200 gm co!!er calorimeter $c % 0.0&3

cal'gm-Co(. )he final tem!erature is "oC. *ind the heat of

fusion of ice. Ans. Lf= 80 cal/g


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#. = beaker of very small mass contains * g of ater at atemperature of $oC. !o many grams of ice at atemperature 8)oC must be dropped in the ater so that the4nal temperature of the system ill be *oCD 6ns7 m 4 89:78; $

*. = copper calorimeter c " .;E/ hose mass is 1) gcontains E* g of ater at )oC. Into these are droppedsimultaneously ) g of aluminum c " .))/ at


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?=@AB >'AB@?%. = glass containing ater is initially of temperature

)-C. (he mass of the glass is 1 g and of speci4cheat .1% cal6g8c - and ater is of mass ) g. If #cubes of ice each of mass 1* g ill be added to theglass of ater, solve for

a/ (he temperature of the mi7ture

b/ (he mass of ice remaining if any

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