Choose the two half-reactions from a table of standard reduction potentials that most closely approximate the reaction that occur within the battery (Pacemaker). What is the standard voltage generated by a cell operating with these half-reactions? (i got +3.85V). The actual Voltage is about +3.5V)

2Li(s)+ Ag2CrO4(s)---> Li2CrO4(s)+2Ag(s)
Calculate the voltage at body temperature, 37°C. (How do i determine Q with no concentration or pressure values given)?

The problem asks for "standard" voltage. That, to me, means at so-called standard state which for cells is 1M concn and 1 atm pressure. I looked up Li potential and found something like -3.05 as a reduction and Ag as aboaut 0.8 as an oxdn. Your tables may give numbers that have CrO4^2- in them and it would be better to use those.

To calculate the voltage at a specific temperature, we need to make use of the Nernst equation. The Nernst equation relates the standard cell potential to the actual cell potential taking into account the temperature and the ratio of the concentrations of the participating species.

The Nernst equation is given as:

E = E° - (RT/nF) * ln(Q)

Where:
E is the cell potential at a given temperature
E° is the standard cell potential
R is the gas constant (8.314 J/(mol·K))
T is the temperature in Kelvin
n is the number of electrons transferred in the balanced half-reaction
F is the Faraday constant (96,485 C/mol)
ln(Q) is the natural logarithm of the reaction quotient

In this case, since no concentration or pressure values are given, we can assume the reaction to be at standard conditions, which means Q = 1. Therefore, ln(Q) = 0.

Substituting these values into the Nernst equation, we can calculate the cell potential at body temperature:

E = E° - (RT/nF) * ln(Q)
E = 3.5 V - (8.314 J/(mol·K) * (37+273) K / (2 * 96,485 C/mol)) * 0
E = 3.5 V

Hence, the voltage at body temperature, 37°C, would be the same as the standard voltage, +3.5 V.