Thermodynamics, Position of Equilibrium

This text will use energy surfaces as problem space maps, and also will use the related energy diagrams to explain why a particular reaction may be favorable and how factors influence that favorability. We need to understand why and if a process is energetically downhill to predict whether it has a chance of happening. 

At room temperature, every 136 kcal/mol (5.73 kJ/mol) change in AG° changes the equilibrium constant ATeq by a factor of 10. Thus, we have a quick way to interconvert AG° in kcal/mol to eq at room temperature Divide AG by -1.36 to obtain the exponent of Req conversely, multiply the exponent of ATeq by -1.36 to get AG in kcal/mol. For kJ/mol just use -5.73 instead. 

The ATgq of a proton transfer reaction at 25 C is 10,000. What is AG in kcal/mol  

Answer We can use the formula AG = -1.361og ATeq- Since a Req of 10,000 is also expressed as 10 log ATeq 4. This gives AG = -1.36(4) = -5.44 kcal/mol. A Rgq greater than 1 favors products, and so does a negative AG therefore the negative sign cross-checks. 

Exercise Cover the value of in Table 2.1 and give the approximate /feq from the AG° then cover the AG° and give the approximate AiG° from the /feq- 

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