Given that at 25.0 °C K for HCN is 4.9 x 10-10 and Kb for NH3 is 1.8 x 10-5. calculate Kb for CN and • • K, for NH₂¹. Enter the K, value for CN followed by the K₂ value for NH4+, separated by a comma, using two significant figures. ▸ View Available Hint(s)
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
![### Acid-Base Properties of Salt Solutions
**Salt is an ionic compound** that is produced when a cation and an anion from an acid-base reaction combine, and solutions of salts can be neutral, acidic, or basic, depending on the acid-base properties of the constituent cations and anions.
Since strong acids and bases completely ionize in solution, the reaction essentially runs to completion forming the salt. Therefore, salts formed by the reaction of a strong acid with a strong base are neutral. NaCl formed by the neutralization of NaOH and HCl is a neutral salt.
Salts formed by the reaction of a strong acid with a weak base are acidic, and salts formed by the reaction of a weak acid with a strong base are basic. This is due to the equilibrium the conjugate has with its acid or base. For example, sodium bicarbonate NaHCO₃ contains the conjugate of the weak acid H₂CO₃. The conjugate will reform the acid through the equilibrium:
\[ \text{HCO}_3^- \, (\text{aq}) + \text{H}_2\text{O} \, (\text{aq}) \leftrightarrows \text{H}_2\text{CO}_3 \, (\text{aq}) + \text{OH}^- \, (\text{aq}) \]
and, thus, acts as a weak base. A solution of NaHCO₃ yields a basic solution.
If a salt is derived from a weak acid and a weak base, the pH of the solution depends on the relative acid strength (\(K_a\)) of the cation and base strength (\(K_b\)) of the anion. If \(K_a > K_b\), the solution of the salt is acidic. If \(K_a < K_b\), it is basic. If \(K_a \approx K_b\), it is neutral.
### Part A
Given that at 25.0°C:
- \(K_a\) for HCN is \(4.9 \times 10^{-10}\) and
- \(K_b\) for NH₃ is \(1.8 \times 10^{-5}\).
Calculate:
- \(K_b\) for CN⁻ and
- \(K_a\) for NH₄⁺.
Enter the \(K_b\) value for CN⁻ followed by the](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Feefb1497-b9c5-4c51-aa29-e7bc635506b5%2F9802c664-6337-4236-b2e6-6d803c6deae4%2F3dhn004_processed.jpeg&w=3840&q=75)
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