Thread Tools Display Modes
Old 02-21-2017, 07:53 PM
Join Date: May 2003
Posts: 31
Enthalpy of dissolved CaCl2 and NaHCO3

The question: What's the enthalpy when aqueous CaCl2 and aqueous NaHCO3 are reacted?

The background:
I'm a high school chemistry teacher and we do a lab where we mix calcium chloride and baking soda. Most things on the internet say this is an exothermic reaction. However, I found that (and Flinn agrees) the dissolving of the CaCl2 is highly exothermic, and the dissolving of the NaHCO3 is endothermic. So I had my students dissolve the CaCl2 first, and feel it get warm. I could also have them dissolve the baking soda in a separate container and feel it get cold.

I tried my own experiment of dissolving both, separately, and leaving them to reach room temperature and then mixing them. To dissolve a good amount of baking soda you have to use a good amount of water (only 4.8g dissolve in 50 mL water at 20 degrees C), so I only barely saw the water change from 19.0 to 17.7 degrees C. So I'm guessing the chemical reaction is endothermic, if both were aqueous. Can anyone confirm that?

Note: I dissolved 3g of baking soda in 50mL of water and ~3g CaCl2 in 5mL of water, to make sure it was in excess, and let them sit until they reached room temperature before putting them together in a cheap styrofoam calorimeter with a Styrofaom lid.
Old 02-23-2017, 11:20 AM
Join Date: Dec 2012
Posts: 993
Assuming everything stays in solution, the only net reaction I can think of is 2 HCO3-(aq) → CO32-(aq) + CO2(aq) + H2O(l). And I'm fairly sure that the corresponding decomposition of a solid salt (e.g. 2 NaHCO3(s) → Na2CO3(s) + CO2(g) + H2O(g) ) has a positive ΔH, i.e. is endothermic.
In your case, you would have to add the enthalpy changes (heats of dissolution for the various species and the heat of vaporization for water) to get from aqueous solution to solids/gases and back. I still believe it would end up endothermic though. (I don't have a table of enthalpies at hand, so you'll have to do some math yourself. Good luck!)
Old 02-25-2017, 05:45 PM
Join Date: May 2003
Posts: 31
Hmm. The reaction most people agree upon is 2NaHCO3 + CaCl2 --> CaCO3(s) + 2NaCl(aq) + CO2(g) + H2O(l). I just want to start with aqueous reactants rather than solids, since it seems to me that the heat/enthalpy of dissolution for both solids is significant, and one is + and the other is -. So I'd guess the net ionic equation would be 2HCO3 - (aq) + Ca 2+(aq) --> CaCO3(s) + CO2(g) + H2O(l).

I guess I'm not sure why you have Na2CO3(s), or why I'd need the heat of vaporization of water (40.6 kJ/mol).

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Forum Jump

All times are GMT -5. The time now is 03:47 AM.

Copyright © 2017
Best Topics: oversized plywood euphemisms for peeing gift chopsticks zsalynn whitworth divorce bo diddley riff chicken biskit crackers jeopardy practice tests brake rust bench warrant expiration dexcom g4 charger tooth brushing tablets cops funny episodes one eye names computer lightning really bad eggs febreze for clothes gorilla genitals occidental etymology n apostrophe sloth se7en nose vacuum cleaner nip asian ripping library cds hay roll cornwall accent postal 2 quotes pachelbel christmas canon almond refrigerator nerf airplane forged stamps allstate enterprise three stooges phrases deskunking house asdf meaning 2nd uncle black housekeeper el guero translation can i put vodka in the freezer what is a fake diamond called do you have to dial 1 on a cell phone amazing grace to the tune of house of the rising sun lyrics is uranium dangerous to touch the goggles they do nothing do we eat roosters what to do when stranded with no money how does the cue ball return how much does a 55 gallon tank weigh how soon do antibiotics work why is my direct deposit late 29 inch electric range laser mole removal face cost erection in front of doctor why is my available credit less than my credit limit giving head to girl jury summons sent to wrong address paraphrasing the declaration of independence rifles and pistols that use the same ammo vinyl asbestos tile danger coke and asparagus for kidney stones best size crock pot for 2 home depot free wood pallets do defense attorneys believe their clients biggest human poop in history i lost my mail key it must be love ford commercial polish terms of endearment tony and frances toto batteries for car key remote