Calorimetry

[MedPR]

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Why must a lid be used in a calorimetry experiment?

A. prevent heat loss via conduction
B. "" via convection
C. "" via evaporation
D. "" via radiation

Answer: evaporation



The explanation is that a greater amount of heat is lost through evaporation than convection. Is that just trivia or is there some way to actually conceptualize it?

 

[pfaction]

I also guessed B, what the heck? Maybe they don't want the water in the water bath leaving?

 

[milski]

Why must a lid be used in a calorimetry experiment?

A. prevent heat loss via conduction
B. "" via convection
C. "" via evaporation
D. "" via radiation

Answer: evaporation



The explanation is that a greater amount of heat is lost through evaporation than convection. Is that just trivia or is there some way to actually conceptualize it?

Probably trivia. I got it wrong too. I strong suspect that at high enough pressure convection will win but who knows... 😕

 

[chiddler]

Convection relies on air bumping into solution and carrying away heat as it absorbs energy form it.

The solution will have its vapor pressure above and air will not efficiently carry away energy since there is so much vapor. So air bumps into solution, gets energy, then gets out.

Evaporation is just solution getting out. So it's half of the path of convection.

Besides that, you can answer this question by realizing that convection occurs with our without cap because the sides of the container are in contact with air.

 

[MedPR]

Convection relies on air bumping into solution and carrying away heat as it absorbs energy form it.

The solution will have its vapor pressure above and air will not efficiently carry away energy since there is so much vapor. So air bumps into solution, gets energy, then gets out.

Evaporation is just solution getting out. So it's half of the path of convection.

Besides that, you can answer this question by realizing that convection occurs with our without cap because the sides of the container are in contact with air.

If the vapor and the liquid are in equilibrium wouldn't air take as much energy from the vapor particles as it would if it could come into direct contact with the surface of the liquid?

Why would the minimal convection from the sides of the container support the cap not preventing further convection?

 

[chiddler]

If the vapor and the liquid are in equilibrium wouldn't air take as much energy from the vapor particles as it would if it could come into direct contact with the surface of the liquid?

Why would the minimal convection from the sides of the container support the cap not preventing further convection?

But it's not in equilibrium because it's open to the air. All the vapor can diffuse away from the calorimeter, leaving an exponentially decreasing vapor pressure of solution from the container.

I just realized that what i'm referring to is conduction not convection which is liquid - fluid specific. The solution needs to transfer via conduction to the sides and then convection to the fluid - the air.

However, if we were still talking about both convection and conduction, then I think that if three sides can perform X amount of convection, then one more side won't make much of a difference. Therefore, the more important contributor will more likely be evaporation.

 

[pfaction]

So they want to keep the liquid (water?) from evaporating is that it?

 

[MedPR]

But it's not in equilibrium because it's open to the air. All the vapor can diffuse away from the calorimeter, leaving an exponentially decreasing vapor pressure of solution from the container.

I just realized that what i'm referring to is conduction not convection which is liquid - fluid specific. The solution needs to transfer via conduction to the sides and then convection to the fluid - the air.

However, if we were still talking about both convection and conduction, then I think that if three sides can perform X amount of convection, then one more side won't make much of a difference. Therefore, the more important contributor will more likely be evaporation.

I guess that makes sense. I figured the reaction would be happening too quickly for evaporation to really have any effect.

Thanks!

 

[Temperature101]

Can someone explain again what is convection?

 

[pfaction]

Heat radiating through the air, making it less dense and moving outwards.

 

[Temperature101]

Heat radiating through the air, making it less dense and moving outwards.

Thanks...

 

[MedPR]

Can someone explain again what is convection?

Convection is just heat transfer exclusively by a fluid (liquid or gas). Think of it in terms of a convection oven. Cold air is more dense (more mass in less volume, since the gases are cooler and aren't expanded as much) so it sinks to the bottom of the oven. The heat source (which is at the bottom of the oven) heats up the cold air and as the cold air expands it starts to rise. At the same time, more cold air is starting to sink since it has transferred its heat to the food in the oven. The key things to remember about convection are:

1. Requires a fluid
2. Goes from hot to cold