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Monday, October 15, 2007

Chemistry Questions - Energy Changes

Q)When solid potassium chloride is added to water, the temperature of the mixture falls. What conclusion can be made from this observation?
A. The process is endothermic.
B. The process is exothermic.
C. All solids dissolve with a fall in temperature.
D. Very little potassium chloride dissolves in water.

Anyone would like to share your answers for above Energy Changes questions?

Rgds
Sean
SimpleChemConcepts
Learning Experience with A Difference

10 comments:

illuminate-x said...

It should be A: the process if endothermic. When the temperature of the mixture falls, it means that the atoms making up potassium chloride take in heat from the surrounding liquid (in this case). The temperature of the mixture will then fall. In any case, the dissolving of hydrated salts in water is an endothermic reaction...

I hope I'm right! xD

LinwooD said...

i think it's A

the process is endothermic :)

Anonymous said...

the asn shld be B rite??

lijun(: said...

A.

when the reaction is endothermic, it takes in heat energy, thus the temperature of the surrounding air will fall.

pf said...

i thought it will be b?
cos now it's the temperature of the mixture that falls and not the surrounding temp

ruth said...

I kinda get why some of you think it's B, but it's A. Cause even though their energy level has gone up, it doesn't mean that their temperature goes up. Know what I mean? Energy doesn't exist only just as heat energy. That's why it's A. Does that make sense to you?

Anonymous said...

It is exothermic because the reaction gives out energy. Thus the fall in temperature of the products. You might have confused it with the fact that heat is given out to the surrounding thus the temperature of the surrounding rises.

Spirit-Breaker said...

A. Endothermic. Heat energy is taken in to decrease the temperature.

Sean Chua said...

An endothermic reaction is any chemical reaction that absorbs heat from its environment.

Mixing of Potassium Chloride with water is indeed experimentally proven to a an endothermic reaction. Potassium Chloride takes in heat energy from the solution and thus the temperature of the solution (which is in this case the environment) falls.

Here's a list of examples of endothermic reactions:
- Reaction of barium hydroxide octahydrate crystals with dry ammonium chloride
- Dissolving ammonium chloride in water
- Reaction of thionyl chloride (SOCl2) with cobalt(II) sulfate heptahydrate
- Mixing water and ammonium nitrate
- Reacting ethanoic acid with sodium carbonate
- Photosynthesis (chlorophyll is used to react carbon dioxide plus water plus energy to make glucose and oxygen)

Hope this helps.

Sean
SimpleChemConcepts
"Learning Experience with A Difference"

Anonymous said...

the reaction is endo....because it absorb heat to break bond so the temperature will fall