Phase Change Chemistry Worksheet Heat Energy, Exercises of Chemistry

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!Part 6: Heating/Cooling curv�

H:t·atirti/6@t@li�J 6urVt."

As a snbstance is heated, its partides begin lo move faster and spread apart.. The spè� oflhe particlesis related lo theirkinetic energy. Tbe relatnte position ofthe particles is related lo fheir poten tia1 energy.^ As solids, liquids, and gases are heated, most ofthe energy that is absorbed is com:erted to ki.oetic energy, and the temperature goes up. Bnl as a sobsfance melts orvapo1:izes, ifs particles spread o�t tremendously. As a x-esult, fue energy absorbed produces chauges in. tbe potential energy

of the particles, so the temperature does uot change. as tl1e phase

c4anges. For thai renson, the freezing point and the melting poiclt of a sub�1ance are fue same.

Base yom· answers ro lhe follo\ing qUE·stions ou th e grapl1 below whirh sbows 10.0 kg ofa substanre thaììs wlid al 0°C aud isheated at a constant--rate of 60 kllojouJes per minute.

L'.\o

t>

c__ 1. Wha1 IS ihc �peratureat whichthe

substance canbe botb.in the sobdand tbc liquid plme? 120

·y .____.,., -r:,. � '

0

° C - ()

° C

1?:r-C

D�E 2.

A- Q-_ Q..

0100 Duòng miich lettei:ed inren.-als is die i; 1.11tcmal poreuhal encrgy of the !1^80 snbstance i nc:reasing? (^) t 60 -1----1-----✓------'-...!...--ll----+---

6 - -^

3. (^) � wruch1eneud sn1ci:rnls is tbe � 40 I

q. km enc euel'gy of the pilrt1des lo- 7 = (Y), lì (^) increa s i ng? 20 Q x (c{)"'" :J40 ¼.� o

_____ 4. How much beat is acùled10 the o 4 7 8 12 16

sub.stance from the tlllle II sto_ps melting IO 1he ùn.u.· thai ÌI beg:ins IO boil?

Ttne in rnimJte!l

7X(o

L4ao (^) )'.::_;\ 5. \Vhat lS tlie tota! beat neededIO mdt the wbstrutce (s1aruilg artime O)? Zl\Y-..W --l-L' \Q

l� Wbat i s the tota! heatneeded10 vaponze fhe substaoce (stl.ningar tim e O)?

D-E � \ .

(.J7. (^) \Vhat is liei hea.r ohapociz-atiQD oftbe �uhm-e?

�A_·P),.____^ 8.^ During wbichletteredmtes.'ltls^ is^ ihè substanc:e ,;olid?

t-D

E-F \D

o c..,

.9. Dur:in,g which leneredin1cn-als iç the s:ubstance i ntbe liquidphase?

10. DuriJlg n>bich lerteredim�als i s the substance in the vapor phase'J

11. What is tlte temperature al which th e substance CaJI be both i n the liqtùdandthc vapo,: phase?

24

I Part 7: Temperature Scales

The. K,elvi.t't $eal�

,ve often measure temperatures with the Celsius scale. The Celsius scale canJiave .negative temperatures. This is be('ause il .ìs based on the freezing (^) _ and boiliog• points of water. The freezm_g point of water is arbitrarily assi (^) gned the rnlue of 0°C while the boiling poiol is assigned a ,.une of l 00 °C. 'Ili.ere are 100 equal divisions. Th.is de.termioes ihe size of the Celsius degree. It 15 poss:ible to gel colder rhan the treezing point ofwater. This is \·hy tbere are negative femperalUres in lbe Celsius S(:'ale. The question is, then, how low ('aD tempmrure go'? Lord Kelv111 IJJ)S\·ered thls question io the mid 1880s. Using n Celsius thelllloroeter, Keh·m dete.pnine-d that temperatures cM go as low as-2. 73 °C,butno lower. Thts

means that ihe Celsill5 scale and the Kelvin. scale are rhe s:arne exct>pl for

their^ origin. The zero on the Keh•fu scale 1S absolute zero, whereas the Zl'ro on the Ces:ius scale lS 273 kelvlllS (273 K). Tue relationswp betweeo

The Temperature Limbo

the Keldo and Celsius temperature lS as foUows·

e (^) K= °C+:?73 nnd °C=K-273 '.

"llltl:liiim•=====•=======·�='

Answer the queslioos IJelow basl'd on rour re:idlug end rbe equntioos nbo,e.

l. What are the Celsius equiv:tlenls for eacb of the Keh-in Rmperatures belo\>?

n- 273X 0

°

C

b. 373K (^) \Q.'ì

o G

c. 15 K - 'òi'5�

0 (,,_

d 623K

e. SOK

[. OK

'?Ys

C.!

-\q�pc..

-a1?:Pr..,

� -a7"

g. 500K^ -aaJ

c_,

h. 131{ _òkf)OG

1. 157 K - \I lD

2. What are the Kelv-in equivalents far e:ich of the Celsius te:ruperamres below? + Oìf:;

a. 213•c SL\� 'l, d.^623 °C^ ?filo'(

b. 373 °C l,Ql\w(^ e..^ so^0 c^ '35:)t

(J{fs?1't- f.^ o·c^ a^76 'L

3. H

es the siz: o fthe Kelvin and^ �e(5Cus^ �t;;e �pnre? Explain.

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g,. sow-c