Question

Calculate the standard cell potential at 25 ?C for the reaction

X(s)+2Y+(aq)?X2+(aq)+2Y(s)

where ?H? = -735 kJ and ?S? = -173 J/K .

Express your answer to three significant figures and include the appropriate units.

Answer 1

Anonymousanswered this

$\Delta$ G₀ = -nFE₀

where F is the faraday constant (96500), n is the moles of electrons involved in the reaction (in this case two since X goes from X(0) to X(2+)), and E is the potential (what you're trying to find). You also need

$\Delta$ G₀ =$\Delta$ H₀ - T * $\Delta$ S₀

where T is temperature in Kelvin. Also keep in mind that delta H₀ is usually given in kilojoules while delta S₀ is usually given in just joules. You'll want $\Delta$G₀ to be in joules so you can get your answer in volts so multiply $\Delta$ H₀ by 1000. So:

$\Delta$G₀ = (-735* 1000) - (25+273) * (-173)

$\Delta$G₀ = -683446 joules

Now take that number and use it to solve for E in the first equation.

$\Delta$ G₀ = -nFE₀

$\Delta$ G₀ / (-nF) = E₀

(-683446) / (-(2)(96500)) = E = 3.5412 volts