1. At what temperatures will a reaction be spontaneous if ? r H ? = +62.4 kJ and
ID: 831562 • Letter: 1
Question
1. At what temperatures will a reaction be spontaneous if ?rH? = +62.4 kJ and ?rS? = +301 J/K?
a.
All temperatures below 207 K.
b.
All temperatures above 207 K.
c.
Temperatures between 179 K and 235 K.
d.
The reaction will be spontaneous at any temperature.
e.
The reaction will never be spontaneous.
2. Explain common ion effect with two example.
3. What is buffer solution and how does buffer solution maintains constant PH? Explain your answer with two examples.
160.0 mL of 0.25 M HF with 225.0 mL of 0.31 M NaF. Pka= 3.2
4. Which set of compounds would form a buffer in aqueous solution and why?
CH3COOH and HCCOH
NaF and NaOH
NaCl and KCl
HBr and NaBr
HCl and HClO
HF and KF
NaF and KF
HCN and NaCN
HF and KCN
5. How does common ion and basic anion affect the solubility of a substance? Explain with example.
6.. The solubility of PbI2 in water is 0.62g in 1000ml of water at 25 deg C. What is the value of Ksp for PbI2? Show your calculation.
1. At what temperatures will a reaction be spontaneous if ?rH? = +62.4 kJ and ?rS? = +301 J/K?
a.
All temperatures below 207 K.
b.
All temperatures above 207 K.
c.
Temperatures between 179 K and 235 K.
d.
The reaction will be spontaneous at any temperature.
e.
The reaction will never be spontaneous.
Explanation / Answer
1.c.Temperatures between 179 K and 235 K.
2. T
he common-ion effect is a term used to describe the effect on a solution of two dissolved solutes that contain the same ion.
The presence of a common ion suppresses the ionization of a weak acid or a weak base.
Examples
If both sodium acetate and acetic acid are dissolved in the same solution they both dissociate and ionize to produce acetate ions. Sodium acetate is a strong electrolyte so it dissociates completely in solution. Acetic acid is a weak acid so it only ionizes slightly. According to Le Chatelier's principle, the addition of acetate ions from sodium acetate will suppress the ionization of acetic acid and shift its equilibrium to the left.
NaC2H3O2(s) ? Na+(aq) + C2H3O2-(aq)
HC2H3O2(l) ? H+(aq) + C2H3O2-(aq)
This will decrease the hydrogen ion concentration and thus the common-ion solution will be less acidic than a solution containing only acetic acid.
In addition to it :
common-ion effect, decrease in solubility of an ionic salt, i.e., one that dissociates in solution into its ions, caused by the presence in solution of another solute that contains one of the same ions as the salt. The common-ion effect is an example of chemical equilibrium. For example, silver chloride, AgCl, is a slightly soluble salt that in solution dissociates into the ions Ag+ and Cl?, the equilibrium state being represented by the equation AgClsolid ?Ag++Cl?. According to Le Ch
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