Calculate K for the reactions in Question 1.

Name: Problem 5, Chapter 14: Chemistry Principles and Reactions
Uploaded: 2021-07-06T21:43:20-08:00
Duration: 4 min 44 s
Channel: Eileen Sullivan
Description: Calculate K for the reactions in Question 1.

Key Concepts

Chemical Equilibrium

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of all species involved. Understanding equilibrium is essential for setting up and solving for the equilibrium constant (K) in various chemical reactions.

Equilibrium Constant (K)

The equilibrium constant, denoted by K, quantitatively expresses the ratio of product concentrations to reactant concentrations at equilibrium according to their stoichiometric coefficients. It indicates the position of equilibrium and helps predict the extent to which a reaction will proceed under given conditions.

Law of Mass Action

The law of mass action provides the foundation for writing the equilibrium constant expression. It states that at equilibrium, the rate of the forward reaction equals the rate of the reverse reaction, and the equilibrium concentrations of the reactants and products are related by a specific ratio raised to the power of their respective stoichiometric coefficients.

Reaction Stoichiometry

Reaction stoichiometry involves the balanced chemical equation of a reaction, which dictates the proportion in which reactants combine and products form. The stoichiometric coefficients from the balanced equation are used as exponents in the equilibrium constant expression, directly influencing the calculation of K.

Transcript

00:01 Okay, so we're going to try to calculate some ks.

00:04 In this first one, we're going to have a little bit of work to do.

00:08 Please assume that all substances are aqueous unless i indicate otherwise.

00:14 So we don't have to write aqueous quite so many times.

00:18 So we're going to try to find the k for this reaction.

00:22 So what i'm going to need to do is find some reactions that will add up to give me that reaction.

00:27 So for instance, i could look at ammonia and write the heart.

00:33 Hydrolysis reaction for that, right? react it with water and it will give me nh4 plus and oh h minus and the k for this reaction will simply be the kb for nh3.

00:51 I'm going to do something similar with the hf.

00:54 I'm going to take the hf and write a hydrolysis reaction with water.

01:03 So we're going to make hydronium ion and f minus.

01:09 Now the k for this reaction is simply the k a for hf for hf but i also need to get rid of my h3o pluses and my waters.

01:22 So i'm going to add in a reaction here where i take hydroxide and hydronium ion, and those will produce two waters.

01:35 I'm going to try and get those three equations, see if they've added up to what i want.

01:40 For that equation that i just wrote, can you see that it's the opposite of the ionization of water? so this is just going to be one over kw.

01:51 So let's show that this all cancels out, right? the two waters cancel out with these two waters.

01:58 This hydroxide cancels out and this hydronium cancel out.

02:02 And i'm left with the equation i'm looking for.

02:05 So if i can add up three equations to equal a fourth, then the k for that fourth reaction simply equals the others all multiplied.

02:13 So it's going to be kb times that ka times 1 over kw...

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