Jan 18, 2010
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Hi All,

I was doing some practice probs and couldn't seem to get a couple answers. If you have any ideas plz help me out!

1. If a reaction occurs spontaneously, which of the following will increase?

a. Internal Energy b. Gibbs Free Energy c. Temperature d. Pressure

The Ans given is Gibbs Free Energy. I thought that G < 0 for reactions that are spontaneous.

2. If 50 ml of 0.5 N HCl reacts 50 mol of .25N of NaOH, then what will be the concentration of HCl after the reaction is complete?

a. 0.9N b. 0.6N c. 0.3N d. 0.13N

I know that is has to be acidic because the concentration of the acid is more for the equal amts of solution.

Tks!
 

pharmD eighty7

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Hi All,

I was doing some practice probs and couldn't seem to get a couple answers. If you have any ideas plz help me out!

1. If a reaction occurs spontaneously, which of the following will increase?

a. Internal Energy b. Gibbs Free Energy c. Temperature d. Pressure

The Ans given is Gibbs Free Energy. I thought that G < 0 for reactions that are spontaneous.

2. If 50 ml of 0.5 N HCl reacts 50 mol of .25N of NaOH, then what will be the concentration of HCl after the reaction is complete?

a. 0.9N b. 0.6N c. 0.3N d. 0.13N

I know that is has to be acidic because the concentration of the acid is more for the equal amts of solution.

Tks!
Are those N's in part 2 suppossed to be M's? and is the 50 mol suppossed to be ml's?
 

chemguy79

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The N's should be correct because it's Normality instead of Molarity. (Similar in concept and N = M in this instance, but not always.)

However, the mol should be mL.
 

aznsensazn3

Pharmacist
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Feb 10, 2010
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Hi All,

I was doing some practice probs and couldn't seem to get a couple answers. If you have any ideas plz help me out!

1. If a reaction occurs spontaneously, which of the following will increase?

a. Internal Energy b. Gibbs Free Energy c. Temperature d. Pressure

The Ans given is Gibbs Free Energy. I thought that G < 0 for reactions that are spontaneous.

2. If 50 ml of 0.5 N HCl reacts 50 mol of .25N of NaOH, then what will be the concentration of HCl after the reaction is complete?

a. 0.9N b. 0.6N c. 0.3N d. 0.13N

I know that is has to be acidic because the concentration of the acid is more for the equal amts of solution.

Tks!
You're right that the gibbs free energy has the be negative in order for it to be spontaneous. But lets think of it this way. In order for it to be spontaneous to the right, delta G has to be negative. When delta G is positive, it is nonspontaenous to the right. When it is 0, the reaction is at equilibrium. All reactions will go toward equilibrium at some point. So back to the question, when the reaction is spontaneous, delta g is negative and going towards equilibrium (0). The gibbs free energy is increasing to go from negative to zero. Hence that's your answer.

For question 2, like the above posters, N is normality. Since in this case the acid and base are monoprotic, (the ionic charge when it becomes dissociated is 1) it's pretty much the same thing as molarity only in this case. You first find how many moles of acid and base you have, and then you neutralize them because it's a strong acid and strong base. So you'll have 25 mmol of H+ and 12.5 mmol of OH-. The 12.5 mmol of OH- will neutralize 12.5 mmol of H+. So you will only have 12.5 mmol of H+ left in solution. Then you divide by the total volume to find the concentration of H+, so 12.5mmol/100mL = 0.13 N HCl.

I think I did that right. Someone let me know if it's wrong.
 
Jan 18, 2010
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Hi aznsensazn3,

Thanks so much for such a detailed explanation! It did help me out :)