# Determining the Gibbs Free Energy change in moving a molecule from inside to outside the cell

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1 Determining the Gibbs Free Energy change in moving a molecule from inside to outside the cell (or vice versa) Since most students got this problem wrong on the second exam, I thought it might be helpful to show some more examples before the final. The equations given at the second exam are copied below. These are the equations for moving sodium from the outside to the inside of the cell. We are going to calculate the delta G to move a sodium ion from the inside to the outside . One important concept to remember when calculating delta G is that the sign depends upon the direction of movement of the ion. I suggest you start each problem by looking at the concentration gradient, and the electrical gradient, and determining whether delta G should be positive or negative. The problem: calculate the energy required to move a sodium ion from inside to outside. The solution: break it up into two parts, G c and G m . Note that G m does not care about the concentration gradient, only whether the molecule is positive or negative. Likewise, G c does not care what the charge of the ion is, only the concentration gradient. m c G G G nFE G m in out c Na Na RT G ] [ ] [ ln m c G G G
2 Looking at the diagram on the left it is evident that G c will be positive because you are moving Na
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