Pottox—A New Thermo-Chemical Notation. 503 
Let ECuO = 87:21, cHN Oy 27K: 
and E[CuO + 2HNO; = Cu(NO,): + H,0] = 15K°*. 
— CuO - 2EH NO; + ECu(NO,), + EH,O = 15K°. 
&Cu(NOs): = 15 + CuO + 2EHNO; - €H.0, 
= 15+ 37:2 + 54:2 — 69, 
= 374K. 
5. Given the thermal quantities 
gH = — 6:2K°, HI = + 13:2, 
EHS =+46K°, cH. db BEAK, 
prove that the reaction 
SHI+S2HS+L 
is thermally reversible, according to whether the substances be dry 
or in solution. 
g[H.S +21 =2HI +8] =a, 
- €H,8 - 21+ 2GHI+éS = 2, 
SOD) (ADA aA Se 
LUD =o & 
A positive quantity, the reaction is therefore thermally pro- 
bable. If we reverse the equation and change the states, we have 
é[2H1 +1 = HS lly] = & 
Ea 22H = 854 EHS + €I, = 2, 
+124-0 +46 +0 = 2, 
+ 17:0 
Hv. 
An almost equal evolution of heat in the opposite direction, conse- 
quent upon the change of state. We may therefore anticipate 
that the reaction will be reversible according as the substances 
are dry or in solution. 
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