Keep the Heat B/Thermodynamics C

[hmcginny]

Hey guys!
I have a question about the plots. It says you are graded for the unit intervals. Should my team just include 20-40 min in ones or 1-40 min in twos for the x axis?(elapsed time). Also, is a temperature of 55 Celsius good after 40 min, starting temperature of 87 Celsius, 100 mL? ( in room temperature)

I think that both ways of graphing your data should be accepted with full credit. I've always just done from 20-40 on my graphs and I've never lost points for them as far as I know. A bit hard for me to judge if thats a good or bad temperature, I've heard of scores both higher and lower than that. It would probably be middle of the pack, but I've only overheard some other team's temperatures at competition and those were all C division, so I'm a bad source for that judgment.

How should students prepare for this event?
Any topics that students should focus on?
What are possible topics to be tested on for the states compitition?

The wiki page (http://scioly.org/wiki/index.php/Keep_the_Heat) is a good starting point. Any chemistry textbook should have a section on thermochem, though for division B, I'd guess you'd only need the basics from that. The rules have a list of topics, though a good number of them are rather vague. Googling those topics should yield some other useful websites. Be careful not to get sucked into the overly complicated stuff, I read this weird college thermo textbook last year and then none of it showed up on any tests at competition.

[retired1]

We included the actual data to the left of the graph which makes it far easier to go to exact data rather than the graph. It also takes up less room than the graph which is included more as an indicator of what is happening than a practical tool. AND, it is required. You can very quickly got to a given time and pull off an accurate temp.

[ScienceOlympian]

Thanks! I did my plots, but they were curving instead of linear. I think did something wrong. Is any of yours graphs curving like a Iog or a 2^x graph? I think I should re do my old plots (took 160 min) sShould I? Is this a good formula for predicting the temperature? Start temp - slope of line multiplied by the time. How do you find the slope of every line, (100,120,150mL)
Sorry for asking too much questions^_^
How would you make a formula for a curved plot? I can't figure it out.

[DivineBbbbbeast]

Thanks! I did my plots, but they were curving instead of linear. I think did something wrong. Is any of yours graphs curving like a Iog or a 2^x graph? I think I should re do my old plots (took 160 min) sShould I? Is this a good formula for predicting the temperature? Start temp - slope of line multiplied by the time. How do you find the slope of every line, (100,120,150mL)
Sorry for asking too much questions^_^
How would you make a formula for a curved plot? I can't figure it out.

No, your plots should be logarithmic. Hot things cool much faster than things that are already near equilibrium temperature (look up Newton's law of cooling, but I doubt you'll need that stuff for Div B). Therefore, the temperature drop over time decreases the longer your trial goes. Try typing up your data in excel and graphing it. Then, have excel graph a trend line and select the logarithmic option. Excel should also give you the equation of the trend line. Or, you can try buying expensive programs that make complicated equations out of the data for you. The former is probably the easier, safest approach. The latter may give you really accurate results depending on the consistency of your box, or it'll give you really wrong predictions.

[TheLeftEye]

No, the graph shouldn't be linear and should be logarithmic. I got the formula and used it for years. The closer the temperature of the water gets to room temerature, the slower it will cool down, until it will just stop cooling completely. But the fromula has a lot of undetermined variables that you have to put into it. The formula is:
(T0-Tr)(e^-kT0) +T0 and to compute K I graphed (for a constant volume of liquid) and took the K out of the formula given by Excel. Also, becuase it's not so obvious: T0 is the starting temp of the water in beaker, Tr is room temp, e is e and k is the constant. I have used this formula for years and it works every time.

[ScienceOlympian]

No, the graph shouldn't be linear and should be logarithmic. I got the formula and used it for years. The closer the temperature of the water gets to room temerature, the slower it will cool down, until it will just stop cooling completely. But the fromula has a lot of undetermined variables that you have to put into it. The formula is:
(T0-Tr)(e^-kT0) +T0 and to compute K I graphed (for a constant volume of liquid) and took the K out of the formula given by Excel. Also, becuase it's not so obvious: T0 is the starting temp of the water in beaker, Tr is room temp, e is e and k is the constant. I have used this formula for years and it works every time

How do you find e? And I do not understand what k is. Thanks.

[ScienceOlympian]

No, the graph shouldn't be linear and should be logarithmic. I got the formula and used it for years. The closer the temperature of the water gets to room temerature, the slower it will cool down, until it will just stop cooling completely. But the fromula has a lot of undetermined variables that you have to put into it. The formula is:
(T0-Tr)(e^-kT0) +T0 and to compute K I graphed (for a constant volume of liquid) and took the K out of the formula given by Excel. Also, becuase it's not so obvious: T0 is the starting temp of the water in beaker, Tr is room temp, e is e and k is the constant. I have used this formula for years and it works every time.

I have Open Office Calc. Is that almost the same?

[ScienceOlympian]

Thanks! I did my plots, but they were curving instead of linear. I think did something wrong. Is any of yours graphs curving like a Iog or a 2^x graph? I think I should re do my old plots (took 160 min) sShould I? Is this a good formula for predicting the temperature? Start temp - slope of line multiplied by the time. How do you find the slope of every line, (100,120,150mL)
Sorry for asking too much questions^_^
How would you make a formula for a curved plot? I can't figure it out.

No, your plots should be logarithmic. Hot things cool much faster than things that are already near equilibrium temperature (look up Newton's law of cooling, but I doubt you'll need that stuff for Div B). Therefore, the temperature drop over time decreases the longer your trial goes. Try typing up your data in excel and graphing it. Then, have excel graph a trend line and select the logarithmic option. Excel should also give you the equation of the trend line. Or, you can try buying expensive programs that make complicated equations out of the data for you. The former is probably the easier, safest approach. The latter may give you really accurate results depending on the consistency of your box, or it'll give you really wrong predictions.

How do you find the equation of different mL in excel? 200 mL cools slower than 100mL. Or is the equation for everything?

[harryk]

I've derived an equation that accounts for initial temp, ambient temp, volume of water, and time. All in one single equation that is based on a value taken from only one calibration plot. Though I'm too selfish to post it

[DivineBbbbbeast]

Thanks! I did my plots, but they were curving instead of linear. I think did something wrong. Is any of yours graphs curving like a Iog or a 2^x graph? I think I should re do my old plots (took 160 min) sShould I? Is this a good formula for predicting the temperature? Start temp - slope of line multiplied by the time. How do you find the slope of every line, (100,120,150mL)
Sorry for asking too much questions^_^
How would you make a formula for a curved plot? I can't figure it out.

No, your plots should be logarithmic. Hot things cool much faster than things that are already near equilibrium temperature (look up Newton's law of cooling, but I doubt you'll need that stuff for Div B). Therefore, the temperature drop over time decreases the longer your trial goes. Try typing up your data in excel and graphing it. Then, have excel graph a trend line and select the logarithmic option. Excel should also give you the equation of the trend line. Or, you can try buying expensive programs that make complicated equations out of the data for you. The former is probably the easier, safest approach. The latter may give you really accurate results depending on the consistency of your box, or it'll give you really wrong predictions.

How do you find the equation of different mL in excel? 200 mL cools slower than 100mL. Or is the equation for everything?

Having a program works well in the sense that it's the only thing you need for predictions, and should work for all the situations. However, usually they get pretty complicated, so you need some hardcore application to write one for you. Unless you want to buy some application like that, you can just make graphs for each of the different mL at different temperatures, and have a trend line for each separate trial. The problem with that is if you have tests at every 25mL interval from like 100mL - 200mL and initial temps of 60- 90 C every 10C , and they give you something like 165 mL 75C, it'll be harder to figure out the final temperature as to if you had a program, which prompts will prompt the user for the different variables. Also, you probably don't want to use other people's equations, b/c everyone has a different box, so a program that works for one person may not work for another.