Is someone able to help me with this?

[GreekMan]

For Chemistry we need to design and perform a practicle to determine the enthalpy of combustion of oly foods. We hve been told that the oily food we will be using is a variety of nuts.

 

We have only just begun learning about enthalpy in Chemistry, and so I am not sure how I to design a method in order to determine the entahlpy of combustion of a nut. Would anybody be able to offer any assistance?

[RyanJ]

For Chemistry we need to design and perform a practicle to determine the enthalpy of combustion of oly foods. We hve been told that the oily food we will be using is a variety of nuts.

 

We have only just begun learning about enthalpy in Chemistry' date=' and so I am not sure how I to design a method in order to determine the entahlpy of combustion of a nut. Would anybody be able to offer any assistance?[/quote']

 

First, welcome to the forums!

 

Well, I guess you could burn the nut and measure the temperature change of the water and then you should know where to go from there

 

Just be careful to extrapolate the temperature to account for heat loss, you'l also need to be careful to mimimize heatloss as much as possible.

 

http://wine1.sb.fsu.edu/chm1045/notes/Energy/Enthalpy/Energy02.htm

 

Good luck!

 

Cheers,

 

Ryan Jones

[woelen]

Measuring the chemical energy, contained in a combustible liquid or solid, in principle is easy. Burn a known ampount of the solid, and use it to heat some known amount of water. The water needs a specific amount of energy per unit of weight to be heated up (appr. 4.2 J/g/K). Using that, by measuring the increase of temperature, one can determine how many Joules of energy are contained in the material to be combusted.

 

The practical setup, however, is not easy at all. A calorimeter should be used. It should be thermally isolated very well. One also has to take into account the heat capacity of the calorimeter (that device also will heat up).

 

And even, if you could measure the amount of energy in the food, by means of combustion, that certainly is not the energy-content of that piece of food for the human body. The human body does not break down the food as far as during the combustion. Many cellulose-like compounds (fibers) are not digested and leave the body more or less unaltered, while at a combustion process these also are burnt.

 

So, there are a lot of practical difficulties and uncertainties with this kind of measurements.

[GreekMan]

We did do a practical on the enthalpy of combustion of certain hydrocarbons. During the lesson i commented on how the values that we calculated from the method that we used would not take into account the heat loss during the practical. However, that was the only practical we will be doing before we have to design this one. So i a really not sure what method to use in order to reduce the heat loss, or how to take into account the heat that is lost during the practical. Would someone be able to explain this to me?

[Prime-Evil]

Bomb Calorimeter would the best way to go. I mean, how often do you get an opportunity to build a bomb in school these days and get credit for it?

 

 

1. Styrofoam cooler.

2. Water initially in balance with room temp/humidity.

3. Thermometer

4. Bomb - small pressure vessel with a removable top, and a valve for pressurizing with air or oxygen, and a fuse wire lead.

5. Small crucible filled with sample of crushed, dried nut.

6. Air or Oxygen Tank

7. Fuse wire

8. Titration kit for NOx

 

Things you need to know:

1. Mass and Specific Heat of Water

2. Mass and Specific Heat of Bomb

3. Mass and Specific Heat of Crucible

4. Mass and Heat of Combustion of Fuse Wire

5. Heat of Combustion of Nitrogen

6. Method for determining Mass of Nitrogen Burned

7. Mass of Nut

 

If you graph the temperature rise after you ignite your bomb you might be able to account for loss through the styrofoam cooler also. Anyhow, what you should be left with in your energy balance is the Heat of Combustion of the Nut. It might not be the same as the calories your body would get if you ate one, but I don't think that was the question.

[Prime-Evil]

We did do a practical on the enthalpy of combustion of certain hydrocarbons. During the lesson i commented on how the values that we calculated from the method that we used would not take into account the heat loss during the practical. However, that was the only practical we will be doing before we have to design this one. So i a really not sure what method to use in order to reduce the heat loss, or how to take into account the heat that is lost during the practical. Would someone be able to explain this to me?

You can mitigate such losses as follows:

 

1. Surround your experiment with water, either completely, or as much as possible. Water has a high specific heat and good thermal conductivity and convection so it will capture most of the heat and achieve constant temperature with everything inside. Everything inside, usually your bomb, needs to be of simple materials so as to be of known mass and specific heat also.

 

2. You can insulate you water tank also, and begin with it at steady state with the room temperature, or even somewhat below so you can graph its temperature rise before you ignite the bomb and use this to account for heat loss to the room once it rise above room temperature. Because of its heat capacity it will not rise that much above room temperature anyway, but you should still be able to quantify heat loss to the environment and reduce your margin of error.

 

Everything else inside the bomb is chemistry. Hope this helps.

[RyanJ]

We did do a practical on the enthalpy of combustion of certain hydrocarbons. During the lesson i commented on how the values that we calculated from the method that we used would not take into account the heat loss during the practical. However, that was the only practical we will be doing before we have to design this one. So i a really not sure what method to use in order to reduce the heat loss, or how to take into account the heat that is lost during the practical. Would someone be able to explain this to me?

 

Asn Prime-Evil said the best method is to isolate the reaction from the environment as much as possible, isolation is the best defence.

 

When we did a simmilar experiment but not involving the conbusion of anything it was through a set of reaction so we has to plot a graph and then read off the point on the graph that corresponded to the initial time of the experiment, the result was extrapolated from the values we had... not the best method but good enough for what we needed.

 

Cheers,

 

Ryan Jones

[rakuenso]

agreed with guy above ^^

 

i think a bomb calorimeter would be most suitable

[RyanJ]

i think a bomb calorimeter would be most suitable

 

^ Second that unfortunatly not all schools have those... if they set this experiment though I guess they do

 

Cheers,

 

Ryan Jones