Answer:
A.)
Explanation:
The general Kb expression is:
In this equation
-----> Kb = equilibrium constant
-----> [HA] = acid
-----> [A⁻] = base
Since liquids are not included in equilibrium expressions, H₂O should not be present. The products are in the numerator while the reactant are in the denominator. In this reaction, CH₃NH₂ is acting as a base and CH₃NH₃⁺ is acting as an acid.
As such, the expression is:
The half-life of the reaction is 50 minutes
Data;
Let the initial concentration of the reaction be X
The reactant left = (1 - 0.45) X = 0.55 X
= X
For a first order reaction
The half-life of a reaction is said to be the time required for the initial amount of the reactant to reach half it's original size.
Substitute the values
The half-life of the reaction is 50 minutes
Learn more on half-life of a first order reaction here;