CHM 11500 Lecture Notes - Lecture 16: Vaporization, Calorimetry

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CHM 11500 Full Course Notes

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Three ways to measure the h(rxn) for a reaction using. Standard entha;pies of formation ( hf) from the elements. The equation below links the value of rh: for a reactionperformed under, if a chemical reaction is reversed, the magnitude of rh remains the same but the sign is reversed. Regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes. No matter which way you do a chemical reaction, if the products and reactants are the same, the change in enthalpy stays the same. Amount of energy needed to break a molecule into its component atoms. Amount of energy you get out when a bond forms. Hrxn=(total energy required to break bonds in reactants)-(total energy released when bonds form)= be(bonds broken)- be(bonds formed) Sublimation is directly turning a solid into a gas.

Related Questions

The standard enthalpy of formation (ÎHâf) is the enthalpy change that occurs when exactly 1 mol of a compound is formed from its constituent elements under standard conditions. The standard conditions are 1 atm pressure, a temperature of 25 âC , and all the species present at a concentration of 1 M . A "standard enthalpies of formation table" containing ÎHâf values might look something like this:

Substance	ÎHâf
H(g)	218 kJ/mol
H2(g)	0 kJ/mol
Sr(s)	0 kJ/mol
Sr2+(aq)	â 549.7 kJ/mol
C(g)	71 kJ/mol
C(s)	0 kJ/mol
N(g)	473 kJ/mol
O2(g)	0 kJ/mol
O(g)	249 kJ/mol
S2(g)	129 kJ/mol

What is the balanced chemical equation for the reaction used to calculate ÎHâf of SrCO3(s)?

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?

CHM 11500 Lecture Notes - Lecture 16: Vaporization, Calorimetry

CHM 11500 Full Course Notes

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