Hi, Does anyone know why when potassium nitrate is added to water, an endothermic reaction occurs?

Answer 1

Good thing the previous answer USED to be a high school chemistry teacher, because he's wrong.

Potassium nitrate does not react with water to form potassium hydroxide and nitric acid. The compound, being the salt of a strong acid and a strong base, has two components which have no acid-base properties, therefore there is no tendency for either to react with water to produce an acid or a base.

In order for something to dissolve, you have to overcome two sets of interactions (solute-solute and solvent-solvent) and form a new one (solute-solvent). Overcoming interactions cost you energy, forming new ones usually gains you energy. In some cases, the energy gained by forming new bonds overcomes what you lost in breaking old ones, so the reaction is exothermic. In the case of potassium nitrate, formation of the new bonds does not gain you as much energy as it cost to break the old ones, therefore it's endothermic, and the heat provided for the dissolution comes from the environment (in this case the water) and the solution gets colder.

KNO3 is not the only salt that does this. NaCl's dissolution is slightly endothermic, as is ammonium nitrate's.

Answer 2

Howdy. I am not a professional Chemist. I am a pharmacist and was once a high school chemistry teacher.
Potassium Nitrate is a salt formed by the reaction of a strong base (Potassium Hydroxide) with a strong acid Nitric acid.
The formation of potassium nitrate is an exothermic reaction.
KOH (aq) + HNO3 (aq) forms KNO3 + H20 + heat
so the reverse will be true
KNO3 + Water + heat will form KOH (aq) + HNO3 (aq)
because KOH is so reactive and so is the HNO3 it will take
lots of energy to form these two products and they must quickly be separated from each other or the equilibrium will
return back to the formation of Potassium Nitrate and Water.
Here is a great memory device an Acid + a base yields a
salt and water.
A similar reaction is HCl (aq) + NaOH (aq) yields NaCl + H20 + heat
HCl is Hydrochloric Acid
NaOH is drano, Sodium Hydroxide, Lye
NaCl is of course Table Salt (Sodium Chloride)
H20 is water
(aq) means aqueous solution which means the chemical is dissolved in water and is forming ions (Cations are positive)
(Anions are negative) for example Na+ is a cation
Cl- is an anion. )

Ready for more fun? Cations (positive ions usually metal ions) are attracted to the Cathode which is the negative
terminal on a battery.
Anions (negative ions which are usually nonmetals) are attracted to the Anode which is the positive terminal on a battery.
Hope you got a charge out of it. Sorry poor pun. Isn't learning fun?

Answer 3

Double displacement reaction takes place....... PbNO(3)2+2KCl=PbCl2+2KNO3