THE CARNOT CYCLE I I ' e i m t t e n f i m George Calingaert, THIS Jam\
\I,.
29, 405-6 (1952)
PREPARATION
Provide ordinary ruhber hand;' approximately ft cm long (12 cm complete loop) and about 2 m m xido
mediately t,o the lips. I t s temperature is now appreeiably below the original. 4. At that point of the cycle hmt will flow from the air to the rubber, bringing it back to its original condit,ion, and compkting the cycle.
DEMONSTRATION
Note by touching the rubber band to the slightly moistened lips that its tempemtiire is about cqiuil to t,li:it of the room. 1 . Stretch it out swiftly as far as it will go without ~re:tkiiig. With good rubber, this will be about four tinier it 5 origi~iiulength. Hold it taut, touch the rubher again 10 the lips, and note that the tcmpmiturc hiis risen iipprcciably. 2. Hold it in this taut position for about 30 seconds; during that time the rubber will be heating the sin-rounding :iir mid will return approximately to room temperaiure. 3 . lielcase the rubber band snddenly hack to its origin:^! ~instrctchcdposition and touch it agaiii im-
REMARKS
It, is shown t,hat energy is used t o "pump" heat to a higher temperature (step I), where it is discharged (step 2). When t,he cooled engine is mad? to "restitute" the work originiilly done t o it, it does so a t the expense of its own heat content (step :3). This cools it below t,he ambient temperature, so that it can now absorb heat from iis surroundings (step 4). If the air we heat is that in the kitchen, while t,he air we cool is inside a )ox, we htivo the familiar household refrigerator. If the air we heat is thai in the living room while the air we cool is that of outdoors-already somewhnt cold- ~we are wing the heat pump to host the house. l o r a more completr diwiis.-iioii. s(-e the reference givcn :ibovc.
COMMON ION EFFECT J i n n i t t i n from C: IT. Soium, T H I ~,TOT I!^ IT,, 25, 489-90 (1948) PREPARATION
Provide two glass cylinders 4 in. in diameter and 19 tall. two 150-ml beakers level full of dry precipitated C'aCO;,, ithout 35 nll of reagent quality sodium :icet:ite crystiils. and 400 ml of 2 !I/ acetic acid. ill.
DEMONSTRATION
Place one 1.50-ml portion of dry CaCO:, in each cyliiider Divide the '2 ¥I ;ç'ct.i acid into two 200-ml portions: dissolve the sodium acetate crystals in one of the 200 nil portions. Add the two portions of acetic acid to the two cylinders at the same time and note, first, the rate at which the foam rises in the two cylinders and, second, the amount of foam formed in each of the two cylinders. REMARKS
Thr foam rises more rapidly in the (yln~derto which the pure acetic acid solution is added than it doe%in
the cylinder to which the acetic acid-sodium ac'etatc solntion is added. However, the total amount of foam formed when all reaction has ceased fin about 3 minutes) is the same. Since the rate of the reaction of an acid with a ci~rhonateis directly proportional to the conceutratioii of hydronium ions, it. is evident from t,his pxperiment that the concentration of h y d r o ~ ~ i uions m in 2 iV acetic acid has been reduced by the presence of the acetate ion. Since the total vohnne of carbon dioxide foam produced in the two cylinders is the same, it is evident that, whereas the acetate ion has reduced the cnncentratioii of hydronium i o w by decreasing the ionization of the acetic acid, it has not altered the total amount of available hydrogeii.
NOTE:0. A. Taliafcrro points out that the desired results :ire obtained only if precipitated calcium carIxmate is used. He suggests Mallinkrodt 4052 light precipit,ated l..Sl', or Baker precipitated powder FSP 1TOO, or Fred I'ortz & Son FSl' light precipitated 2288P.
