Melting and Mass

[Rolling]

Let's say I have a compound that melts at 50 degrees Celsius.

Case1 : I put it in a beaker of water at 100 degrees celsius (this is the temp of the H2O).

Case2 : Let's say I put it in a beaker of water at 90 degrees celsius (this is the temp of the H2O).

This is what I want to know.

I believe that JUST based off of Q=mc(Delta T) that would mean in case 2, MORE time would be required to melt the compound, because more heat would be needed. Please correct me if I'm wrong. Q has the units of Joules, thus meaning PER second, so if I were to decrease the time, I am decreasing the HEAT RATE.

However, would the TIME that the compound takes to melt be DIFFERENT in EITHER case depending on how much water I put in the beaker?

So if I put 500 grams as opposed to 200 grams, that would instead INCREASE the heat rate and THUS speed up the melting process. Is that right?

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[inaccensa]

Let's say I have a compound that melts at 50 degrees Celsius.

Case1 : I put it in a beaker of water at 100 degrees celsius (this is the temp of the H2O).

Case2 : Let's say I put it in a beaker of water at 90 degrees celsius (this is the temp of the H2O).

This is what I want to know.

I believe that JUST based off of Q=mc(Delta T) that would mean in case 2, MORE time would be required to melt the compound, because more heat would be needed. Please correct me if I'm wrong. Q has the units of Joules, thus meaning PER second, so if I were to decrease the time, I am decreasing the HEAT RATE.

However, would the TIME that the compound takes to melt be DIFFERENT in EITHER case depending on how much water I put in the beaker?

So if I put 500 grams as opposed to 200 grams, that would instead INCREASE the heat rate and THUS speed up the melting process. Is that right?

I believe traditionally Q is the amt of heat req to raise the temp of 1g of substance by 1 degree celsius. I'm not sure where you are getting heat rate.I hope someone else can shed light on this concept. I'm not sure that I understand your q. If the compound melts at 50 degrees, wouldn't it melt the instant u add it to water? I don't think the mass of water has anything to do in this case. I'll leave someone else to ans this though.

 

[Charles_Carmichael]

Let's say I have a compound that melts at 50 degrees Celsius.

Case1 : I put it in a beaker of water at 100 degrees celsius (this is the temp of the H2O).

Case2 : Let's say I put it in a beaker of water at 90 degrees celsius (this is the temp of the H2O).

This is what I want to know.

I believe that JUST based off of Q=mc(Delta T) that would mean in case 2, MORE time would be required to melt the compound, because more heat would be needed. Please correct me if I'm wrong. Q has the units of Joules, thus meaning PER second, so if I were to decrease the time, I am decreasing the HEAT RATE.

However, would the TIME that the compound takes to melt be DIFFERENT in EITHER case depending on how much water I put in the beaker?

So if I put 500 grams as opposed to 200 grams, that would instead INCREASE the heat rate and THUS speed up the melting process. Is that right?

Joules is not a per second thing. A joule is a newton*meter. A watt is a joule/sec and is used to measure power. So I'm not sure what you mean by heat rate either.

Remember that in order to completely melt, all the molecules of the solid have to have enough energy (ie. kinetic energy) to overcome the activation energy barrier for the phase change. And also remember that temperature is a quantitative measure of the average kinetic energy. So, the greater the temperature, the greater the average kinetic energy. This means that more molecules are likely to overcome the activation energy barrier and thus, this would mean that a phase change (ie. melting) would occur faster. So, regarding your initial cases, Case 2 would cause the compound to melt a bit slower since the molecules have a lower average kinetic energy than in Case 1.

Regarding the relationship between mass and the melting rate, think about ice cubes and glaciers. If you put a glacier (huge mass) and an ice cube (tiny mass) in water of same temperature, which is likely to completely melt quicker? The ice cube because there is so much less of it to melt. As the amount of material you want to melt increases, you need to put in more energy (ie. heat) in order to increase the average kinetic energy of the molecules high enough to overcome the activation barrier.

Hope this helps.

 

[Rolling]

I'm not talking about the MASS of the compound, I'm talking about the mass of the water.