Temperature changes in mixed solutions

[semi-ambivalent]

Today I had 500ML of water, a hair under 67 degrees, in a graduate. I mixed in 10cc of HC-110 syrup from the same shelf as I got the tempered water. After mixing, the solution was 68 degrees, spot on. Is there a heat releasing reaction going on here when the HC-110 goes into solution? The thermometer was a Kodak color processing model, and reads about a quarter degree below another thermometer that I keep as a benchmark. Never use it, store it on end.

s-a

 

[Photo Engineer]

There can be heating or cooling in most situation where chemicals are mixed. I would not be surprised if the temp went up. You are initiating quite a host of chemical changes when you add HC-110 syrup to water.

PE

 

[Loren Sattler]

I cannot answer your question, but have a comment. I use D76 1:1 with Tri-x 120 and 35mm films. I am diligent about temperature control during development in SS tanks. I measure the developer coming out of the tank and usually find a small increase in temperature, 1/4 to 1/2 degree despite keeping the tank in a bath of tempering water at 68 degrees. This has puzzled me forever.

 

[MattKing]

I cannot answer your question, but have a comment. I use D76 1:1 with Tri-x 120 and 35mm films. I am diligent about temperature control during development in SS tanks. I measure the developer coming out of the tank and usually find a small increase in temperature, 1/4 to 1/2 degree despite keeping the tank in a bath of tempering water at 68 degrees. This has puzzled me forever.

Agitation will also add kinetic energy.

 

[Gerald C Koch]

A lot of interesting things can happen when you mix two liquids. For example when you mix 100 ml of water and 100 ml of alcohol the resulting mixture's volume is less than 200 ml.

 

[Photo Engineer]

Sorry, but this effect is due to a number of forces such as Van der Waals force, Ionic strength, and other things going on when you mix two chemicals, one being liquid and the other a liquid or solid.

If attraction increases, density goes up and volume goes down. It is often a toss up whether temperature goes up or down. For example, Sodium Chloride added to water increases temp very very slightly, but Ammonium Chloride decreases temp. rather profoundly. Density usually goes down with Ammonium salts but stays close to the same or goes up with Sodium salts.

And that is just a rough generalization!

PE

 

[Gerald C Koch]

Among the other things that PE mentions are the change in entropy which occurs when mixing. When considered alone this change will cause a drop in temperature since heat is required. This heat is "stolen" from the mixture and so temperature drops. For solids added to water there is also the heat of hydration to consider. So adding that spoonful of sugar to your coffee is a very complex process.

 

[Gerald C Koch]

Chemistry is not an easy subject. It requires a person to consider many different ideas simultaneously when solving problems. I used to teach freshman chemistry which is usually a 2 or 3 semester course. It was not unusual for a student to drop a letter grade when going from the first semester to the second and again when going from the second to the third. Knowledge builds on what has been learned before. What a student doesn't learn in a previous semester comes back to bite him.