Acid dissociation constant thermicity

In summary, the acid dissociation constant as an equilibrium constant is affected by temperature. The reaction between a general acid and water, represented by HA(aq) + H2O(l) ⇌ A-(aq) + H3O+(aq), can be determined to be exothermic or endothermic by looking at whether Ka increases or decreases with temperature. Generally, the thermicity of the dilution of strong acids is easily noticeable. The reaction is exothermic if the bond enthalpy of HA is greater than that of O-H, and always exothermic when analyzing the net ionic equation.
  • #1
PPonte
The acid dissociation constant as an equilibrium constant is affected by temperature. Right? Thus, could someone tell me if the reaction between a general acid and water:

HA(aq) + H2O(l) ⇌ A-(aq) + H3O+(aq)

is exothermic or endothermic?
I think it is endothermic by similiarity with water auto-ionization reaction.
 
Physics news on Phys.org
  • #2
The thermicity can be determined by whether Ka increases or decreases with temperature.

Practically speaking, I've found with most strong acids, the thermicity of the dilution of the acid is easily noticeable. Whether this is generally true of all acids, I don't know.
 
  • #3
Sorry, but I didn't understand if the reaction is exothermic or endothermic. Ka increases or decreases with higher temperatures?
 
  • #4
Consider which bonds are broken / made

~H
 
Last edited:
  • #5
Then, we broke 1 H-A, 2 O-H and made 3 O-H.

If the reaction is exothermic 3 O-H > H-A + 2(O-H) <=> O-H > H-A
If the reaction is endothermic, O-H < H-A

Right?
 
  • #6
No, you broke a single HA bond and made a single O-H bond, look at your equation.

Edit sorry PPonte, you are right I didn't fully read your post #5, yes the reaction is endothermic if the bond enthalpy of HA is greater than that of O-H.

~H
 
Last edited:
  • #7
The reaction is exothermic.

H+(aq) + OH-(aq) ---> H2O(l) /\H = -57kJmol-1



http://www.wbateman.demon.co.uk/asa2sums/sum2.1/sum2.1.htm" [Broken]
 
Last edited by a moderator:
  • #8
oops sorry
wrong reaction
 
  • #9
I've corrected my post above, aplogies PPonte.

~H
 
  • #10
That's ok, no problem Hootenanny. Thank you for your help.
 
  • #11
In this case, I'm pretty sure that it's always exothermic

hint: analyze the net ionic equation.
 

What is the definition of acid dissociation constant thermicity?

The acid dissociation constant thermicity, also known as the thermic acid dissociation constant, is a measure of the strength of an acid in a solution. It is the equilibrium constant for the dissociation reaction of an acid in water, and is denoted by the symbol Ka. It is a measure of the degree to which the acid dissociates into its ions.

What factors affect the value of acid dissociation constant thermicity?

The value of acid dissociation constant thermicity is affected by several factors. These include the strength of the acid, the temperature of the solution, and the presence of other substances in the solution that may affect the dissociation of the acid. The nature of the solvent and the concentration of the acid also play a role in determining the Ka value.

How is acid dissociation constant thermicity measured?

The acid dissociation constant thermicity is typically measured experimentally by titrating a known concentration of the acid with a strong base. The volume of base required to neutralize the acid is used to calculate the Ka value. Alternatively, it can also be calculated using the equilibrium concentrations of the acid and its dissociation products.

What is the relationship between acid dissociation constant thermicity and pH?

The pH of a solution is related to the acid dissociation constant thermicity through the following equation: pH = -log(Ka) + log([HA]), where [HA] is the equilibrium concentration of the undissociated acid. This means that the lower the value of Ka, the stronger the acid and the lower the pH of the solution will be.

Why is acid dissociation constant thermicity important in chemistry?

Acid dissociation constant thermicity is an important concept in chemistry as it helps us understand the strength of acids and their behavior in solution. It is also used to determine the pH of a solution and to calculate the concentrations of acids and their dissociation products. The Ka value is also useful in predicting the reactions of acids with other substances and in understanding the role of acids in various chemical processes.

Similar threads

  • Biology and Chemistry Homework Help
Replies
1
Views
2K
  • Biology and Chemistry Homework Help
Replies
5
Views
3K
  • Biology and Chemistry Homework Help
Replies
2
Views
2K
  • Biology and Chemistry Homework Help
Replies
1
Views
2K
  • Biology and Chemistry Homework Help
Replies
4
Views
13K
  • Biology and Chemistry Homework Help
Replies
4
Views
3K
  • Biology and Chemistry Homework Help
Replies
17
Views
3K
  • Biology and Chemistry Homework Help
Replies
2
Views
2K
  • Biology and Chemistry Homework Help
2
Replies
48
Views
7K
  • Biology and Chemistry Homework Help
Replies
4
Views
3K
Back
Top