BIOCHEM 523 Lecture Notes - Lecture 3: Jmol, Hydrolysis, Solution

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cerisebuffalo390

16 Sep 2017

School

UMASS-Amherst

Department

Biochemistry & Molecular Bio.

Course

BIOCHEM 523

Professor

James Staros

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Document Summary

Biochem423/523 - lecture 3 - thermic and gonic reactions. An exothermic reaction, one in which the h is negative. If heat has been taken up, the enthalpy ( h) will be positive, and if heat has been released, the enthalpy will be negative. A process with positive enthalpy ( h) is endothermic. A process with negative enthalpy ( h) is exothermic. A process with positive free energy ( g) is endergonic. A process with negative free energy ( g) is exergonic direction) The g only tells you if the reaction is favorable or unfavorable, and the h only tells. Spontaneous, in chemical terms, does not mean speed or celerity of the reaction! you if heat has been released or absorbed. Diffusion is entropy driven: has a positive s. Standard free energy: g and g ". Standard free energy changes, for example, changes in free energy under a defined set of conditions, provide useful reference points:

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Help please

I need help on this chemistry work. Thanks.

DATA ANALYSIS

Using the example, calculate the Gibbs free energy for the process of dissolving ammonium nitrate and the process of dissolving sodium hydroxide (equation: ÎG = ÎH â TÎS).

Use the standard temperature 298 K.

Use the experimental data to calculate enthalpy of dissolving (ÎH).

Use the following data to calculate the entropy change (ÎS):

	S (J/K mol)
NH₄NO₃(s)	151
NH₄⁺(aq)	113.4
NO₃^-(aq)	146.4
NaOH(s)	64.46
Na⁺(aq)	59.0
OH^-(aq)	- 10.7

After completing the calculations answer the following questions separately for each experiment:

Is the dissolving exothermic or endothermic?

Does the entropy decreases or increases during dissolving?

Is the Gibbs free energy positive or negative? Is the process of dissolving spontaneous?

Using data in the appendix in your textbook, calculate Gibbs free energy for the reaction of dissolving

lithium phosphate, Li₃PO₄, in water at 25 Â°C. Do the calculations in two ways:

1) Use standard enthalpy of formation (ÎH) and entropy (S) from the appendix in your textbook, and use the same formula as you did in the lab experiments: ÎG = ÎH â TÎS. Remember that both ÎH and ÎS has to include three lithium ions.

2) Use standard free energies of formation from Appendix 6 (ÎG) and equation

ÎG = âÎG _products â âÎG _reactants

Are the results similar in both calculations?

In the following reactionCH4+CH4 arrow CH3CH3+H2two C-H bonds are broken(bond energy =412 kj/mol) to form a new C-C bond(bond energy=348 kj/mol and a new H-H bond(bond energy=436 kj/mol). Estimate the enthalpy in this reaction. Is it endothermic or exothermic:Hint for exothermic reactions the combined energies of the new bonds should be larger than the combined energies of the broken bonds.Balanced the following unbalanced reaction and calculate its standard free energy change(under standard reactions). State whether the reaction is spontaneous or nonspontaneous under standard conditionsC2H5OH(l)+O2(g) arrow CO2(g)+H2O(l) C2H5OH(l) O2(g) CO2(g) H2O(l) deltaH kj/mol -277.7 0 -393.5 -285.8 deltaG kjmol -174.8 0 -394.4 -237.1

BIOCHEM 523 Lecture Notes - Lecture 3: Jmol, Hydrolysis, Solution

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