It is called a hypothesis.
Answer:
Since with LiBr no precipitation takes place. So, Ag+ is absent
When we add Li2SO4 to it, precipitation takes place.
Ca2+(aq) + SO42-(aq) ----> CaSO4(s) ...Precipitate
Thus, Ca2+ is present.
When Li3PO4 is added, again precipitation takes place.Reaction is:
Co2+(aq) + PO43-(aq)---->Co3(PO4)2(s) ... Precipitate
A. Ca2+ and Co2+ are present in solution
B. Ca2+(aq) + SO42-(aq) ----> CaSO4(s)
C. 3Co2+(aq) + 2PO43-(aq)---->Co3(PO4)2(s)
Separa los metales de los no metales. Agregame como amiga, saludos.
This question is describing the following chemical reaction at equilibrium:
![A\rightleftharpoons B](https://tex.z-dn.net/?f=A%5Crightleftharpoons%20B)
And provides the relative amounts of both A and B at 25 °C and 75 °C, this means the equilibrium expressions and equilibrium constants can be written as:
![K_1=\frac{90\%}{10\%}=9\\\\K_2=\frac{20\%}{80\%} =0.25](https://tex.z-dn.net/?f=K_1%3D%5Cfrac%7B90%5C%25%7D%7B10%5C%25%7D%3D9%5C%5C%5C%5CK_2%3D%5Cfrac%7B20%5C%25%7D%7B80%5C%25%7D%20%20%3D0.25)
Thus, by recalling the Van't Hoff's equation, we can write:
![ln(K_2/K_1)=-\frac{\Delta H}{R}(\frac{1}{T_2} -\frac{1}{T_1} )](https://tex.z-dn.net/?f=ln%28K_2%2FK_1%29%3D-%5Cfrac%7B%5CDelta%20H%7D%7BR%7D%28%5Cfrac%7B1%7D%7BT_2%7D%20-%5Cfrac%7B1%7D%7BT_1%7D%20%29)
Hence, we solve for the enthalpy change as follows:
![\Delta H=\frac{-R*ln(K_2/K_1)}{(\frac{1}{T_2} -\frac{1}{T_1} ) }](https://tex.z-dn.net/?f=%5CDelta%20H%3D%5Cfrac%7B-R%2Aln%28K_2%2FK_1%29%7D%7B%28%5Cfrac%7B1%7D%7BT_2%7D%20-%5Cfrac%7B1%7D%7BT_1%7D%20%29%20%7D)
Finally, we plug in the numbers to obtain:
![\Delta H=\frac{-8.314\frac{J}{mol*K} *ln(0.25/9)}{[\frac{1}{(75+273.15)K} -\frac{1}{(25+273.15)K} ] } \\\\\\\Delta H=4,785.1\frac{J}{mol}](https://tex.z-dn.net/?f=%5CDelta%20H%3D%5Cfrac%7B-8.314%5Cfrac%7BJ%7D%7Bmol%2AK%7D%20%2Aln%280.25%2F9%29%7D%7B%5B%5Cfrac%7B1%7D%7B%2875%2B273.15%29K%7D%20-%5Cfrac%7B1%7D%7B%2825%2B273.15%29K%7D%20%5D%20%7D%20%5C%5C%5C%5C%5C%5C%5CDelta%20H%3D4%2C785.1%5Cfrac%7BJ%7D%7Bmol%7D)
Learn more: