Heat Of Combustion Of Candle Wax 28386j

Heat of Combustion of Candle Wax The amount of heat released by the complete combustion of one mole of a substance is defined as the heat of combustion, ΔHcomb. The amount of heat released may be measured in calories (cal) or in joules (J). A calorie is the amount of heat needed to raise the temperature of one gram of water one degree Celsius. The SI unit of heat is the joule. One calorie = 4.184J If a sample of pure carbon is burned in oxygen, the reaction is as follows: C(s) + O2(g) → CO2(g) ΔHcomb = -393.5 kJ Some additional heats of combustion are provided in the table. Heats of Combustion Substance Formula ΔHcomb (kJ/mol) Methane (g) CH4 -890.3 Propane (g) C3H8 -2219.9 Butane (g) C4H10 -3536.1 Octane (l) C8H18 -5450.8 In this activity, you will calculate the heat of combustion of the fuel in a candle. The burning candle will heat a measured quantity of water. Using the specific heat of water, the mass of the water, and the increase in temperature, you can calculate the amount of heat released by the burning candle using the following relationship: Quantity of heat in joules = (mass of water)(change of temperature)(specific heat of water), where the specific heat of water is J/(g.°C). You can then calculate the moles of candle wax that burned to obtain the heat of combustion (ΔH comb) in kJ/mol. Problem How can you measure the heat released by a burning candle and calculate the heat of combustion of candle wax? Objectives • Measure the change in temperature of a mass of water during a combustion reaction. • Calculate the amount of heat released during a combustion reaction. • Calculate the energy released per mole of reactant during a combustion reaction. Materials Candle Small metal can Large metal can 1/2 in. steel nuts (4) thermometer balance felt-tip marker metric ruler Paper clips (2) Matches Ring stand Ring Thermometer clamp Glass stirring rod

Safety Precautions • Always wear safety goggles. • Dispose of wax wastes as directed by your teacher. • Hot objects may not appear to be hot. • Open flames may ignite clothing or hair. Pre-Lab 1. Define heat of combustion and specific heat 2. State the relationship between joules, mass of water, change of temperature, and specific heat. 3. Define exothermic and endothermic reactions. What is the sign of ΔH for an exothermic reaction? An endothermic reaction? 4. Explain how you can calculate the heat of combustion if you know the number of joules released, the mass of substance burned, and the molar mass of the substance. 5. Compare the heats of combustion in the chart on page 1 of the lab. Which would you rather have stranded in the snow? Why? 6. Diesel engines are often used in large trucks because the diesel fuel produces more heat per liter than gasoline. What does this imply about the nature of the molecules of diesel fuel compared to gasoline (octane)? Procedure 1. Light a candle and drip a few drops of molten wax onto a can lid Attach the candle to the lid while the wax is liquid and blow out the candle. 2. Determine the mass of the candle and lid and record this value in a Data Table. 3. Refer to Figure A as you set up the apparatus. Unbend three paper clips so that they are each in the shape of an S-hook. Use the paper clips to attach the small can to the ring. 4. Position the candle assembly under the small can and adjust the ring so that the bottom of the can is 4 or 5 cm above the top of the unlighted candle. 5. Unhook the small can. Measure the mass of the can and record this value in Data Table 1. 6. Fill the can approximately half full of distilled water. 7. Measure and record in Data Table 1 the mass of the can and the water. 8. Place the large can over the candle. 9. Raise the large can off the base of the ring stand and insert the four nuts evenly spaced under the can. This will allow air needed for the combustion of the candle to enter around the base of the can. 10. Record the initial temperature of the water in your Data Table. Use a match to light the candle. 11. Immediately replace the small can and water in its previous position. Time the experiment for 10 minutes. 12. While the candle heats the water, gently stir the water with a glass stirring rod. 13. Blow out the candle and record in the Data Table the final temperature

of the water. 14. Measure the final mass of the candle assembly and record in your Data Table. Heat of Combustion of Candle Wax Data and Observations Initial mass of candle assembly (g) Final mass of the candle assembly (g) Mass of the empty can (g) Mass of the small can and water (g) Initial temperature of water (°C) Final temperature of water (°C) Calculations Mass of the candle burned (g) Mass of the water (g) Change in temperature of the water (°C) 1. Calculate the number of joules of heat absorbed by the water. Convert to kilojoules. 2. Assume that the formula for wax in the candle is C32H66.. Find the moles of the candle burned. 3. Calculate the heat of combustion for wax. The accepted value is around 13,000kJ. There is variability in the components of wax so this is not an exact amount.

The Hydrocarbon composition of the wax varies and is a mix of C20 to C40 so an exact equation can not be given. However, it is a standard combustion reaction. i.e. CxHy + (x + y/4) O2 ---> (y/2) H2O + (x) CO2 The little numbers (subscripts) are coefficients. A chemistry reaction is like a math equation: whatever is on one side has to equal whatever is on the opposite side. The coefficients take care of that. They look confusing in the reaction shown because they are letters, but if you stick numbers in there it would be much easier to understand. Let us use an example of C25 which would be C25H52. C25H52 + 38 O2 ------- 25CO2 + 26 H2O + energy (heat and light) When you burn a candle, you are performing simple combustion reactions of this type. The oxygen comes from the air and the heat initially comes from an outside source such as a match. When this combustion reaction happens, it makes water and carbon dioxide as shown as well as heat and light energy. The coefficients tell us how much of each component is used and produced. The wick in a candle is also mainly hydrocarbon with oxygen also present and this also burns though at a much slower rate. When you light the wick, you provide a heat source and oxygen from the air. The smoke formed contains carbon dioxide and water and also some soot from inneficient combustion. Read more: http://wiki.answers.com/Q/What_chemical_reactions_occur_during_candle_burning#ix zz1zexAdQY1

How to find out Oxygen ratio in air by Candle combustion Rate this item (0 votes)

How to find out Oxygen ratio in air by Candle combustion Pakistan Science Club How to find out Oxygen ratio in air by Candle combustion Materials candle, glass vessel or PET bottle, match, plate, sodium hydroxide, and water Procedure 1. The sodium hydroxide is dissolved in water and the solution of 3% is made. 2. The candle is fixed in the plate. 3. Light the candle. 4. Cover it with the glass vessel or the PET bottle. 5. Confirm the water level and the ratio of the volume. Science When burning, the candle uses the oxygen in the air. The water made by burning reduce the volume about 1/1700 after cooling and becoming the liquid. As for remaining carbon dioxide, it reacts with the sodium hydroxide and the sodium carbonate is made. It is absorbed to the solution. Therefore, water which is almost same volume of the oxygen rises in the container.

Why does the water rise? It's a very popular experiment (eg), from elementary school : put a burning candle on a dish filled with water, cover the candle with an inverted glass: after a little while, the candle flame goes out and the water level inside the glass rises. The standard explanation (as I recall it) was that combustion "burns" oxygen, and the consummed volume s for the extra water that goes inside the glass. Is this correct? I feeling (years later) uncomfortable with the up vote 9 explanation, because "to burn" is certainly not "to dissapear": I thought that down oxygen combustion produces (mainly) CO2 and hence one oxygen molecule vote would produce another CO2 molecule, and the volume would remain basically favorit the same. Perhaps CO2 dissolves into the water? I would doubt that. e

To add to my confusion, others state that the main cause is not the oxygen combustion but the changes of air temperature, that decreases when the flame goes out and makes the air inside the glass contract... which would rather invalidate the experiment as it was (and is) traditionally taught to students. What is the right explanation?

(image from here) Update: As from webpage linked in accepted answer, there are several effects here, but I think it's safe to say that the "traditional" explanation (consumption of oxygen) is just wrong: oxygen turns into CO2 and water and -even assuming that this is the complete chemical picture (it's not) and that all water condensesthat would produce a slight decrease of volume (CO2 dissolves in water poorly and very slowly). The main effect here is thermal expansion-contraction of air.

4 Answers active oldest votes up vote 7 I found two web pages that explain the phenomenon quite well, and even

looks into the misconceptions people have. The candle flame heats the air in the vase, and this hot air expands. Some of the expanding air escapes out from under the vase — you might see some bubbles. When the flame goes out, the air in the vase cools down and the cooler air contracts. The cooling air inside of the vase creates a vacuum. This imperfect vacuum is created due to the low pressure inside the vase and the high pressure outside of the vase. We know what you're thinking, the vacuum is sucking the water into the vase right? You have the right idea, but scientists try to avoid using the term "suck" when describing a vacuum. Instead, they explain it as gases exerting pressure from an area of high pressure to an area of low pressure. A common misconception regarding this experiment is that the consumption of the oxygen inside of the bottle is also a factor in the water rising. Truth is, there is a possibility that there would be a small rise in the water from the flame burning up oxygen, but it is extremely minor compared to the expansion and contraction of the gases within the bottle. Simply put, the water would rise at a steady rate if the oxygen being consumed were the main contributing factor (rather than experiencing the rapid rise when the flame is extinguished).(1) The page from Harvard goes into more detail on the argument versus the error for the incorrect statement.

down vote accepted Argument: Oxygen is replaced by Carbon dioxide. So, there is the same

amount of gas added than taken away. Therefore, heat alone most be responsible for the water level change. Source of the Error: A simplified and wrong chemical equation is used, which does not take into the quantitative changes. The chemical equation has to be balanced correctly. It is not true that each oxygen molecule is replaced by one carbon dioxide molecule during the burning process; two oxygen molecules result in one carbon dioxide molecule and two water molecules (which condense). oxygen is present in the air as a diatomic molecule. [A reader clarifies the water condensation in an email to me as follows: If the experiment were done with the sealing fluid able to a temperature greater than 212 F and the whole system held above this temperature then the water product of combustion would remain gaseous and the pressure within the vessel would increase as a result of three gaseous molecules for every two prior to combustion and the sealing fluid would be pushed out.] Argument: Carbon dioxide is absorbed by the water. Thats why the oxygen depletion has an effect. Source of the Error: This idea is triggered from the fact that water can be carbonized or that the oceans absorb much of the carbon dioxide in the air. But carbon dioxide is not absorbed so fast by water. The air would have to go through the water and pressure would need to be applied so that the

carbon dioxide is absorbed during the short time span of the experiment. Argument: The experiment can be explained by physics alone. During the heating stage, air escapes. Afterwards, the air volume decreases and pulls the water up. Source of the Error: the argument could work, if indeed the heating of the air would produce enough pressure that some air could leave. In that case, some air would be lost through the water. But one can observe that the water level stays up even if everything has gone back to normal temperature (say 10 minutes). No bubbles can be seen. Argument: It can not be that the oxygen depletion is responsible for the water raising, because the water does not rise immediately. The water rises only after the candle dims. If gas would be going away, this would lead to a steady rise of the water level, not the rapid rise at the end, when the candle goes out. Source of the Error: It is not "only" the oxygen depletion which matters. There are two effects which matter: the chemical process of the burning as well as a physical process from the temperature change. These effects cancel each other initially. Since these effect hide each other partially, they are more difficult to detect. (2) It clearly has more to do with the temperature differences than any conversion of gases. Especially considering that a volume of oxygen and carbon dioxide will be nearly identical to human eye observation. answered Jan 4 at 3:07

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edited Jan 4 at 23:42

Larian LeQuella 4,72621438 4

I'd trust Harvard (second footnote I am guessing). – Skava Jan 4 at 3:11

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Yes "Skava", now go to bed! – Larian LeQuella Jan 4 at 3:12

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This answer is useful in pointing the best explanation I've seen (the second link), but the text is plainly copied other pages (should be formatted as quotes) and does not make clear the general summary/conclusion. – leonbloy Jan 4 at

13:49 I'd question one thing from that answer, though: Nowhere is a vacuum created. There's always air in the glass, and it always fills the whole space not occupied by water. When the air cools down, it doesn't contract by itself, only its pressure goes down (intuitively: Since the molecules get slower, they hammer less onto the water surface). As result the water is pressed more in by the air outside than out by the air inside, and thus flows inside. This rising water compresses the air inside, which causes air density and thus pressure inside to rise again until equilibrium is reached. – celtschk Jan 18 at 5:47 up I have not actually tried this experiment, but I will make at least a few vote 4 observations: down vote Hypothesis 1: The burning of oxygen is responsible for the reduced air pressure.

Prediction - if the burning of oxygen is the sole cause of the change in pressure, we should expect to see the water in the glass rise at a more or less constant rate from the moment the environment is sealed until the burning stops. After the candle extinguishes, there should be no more change in water level. Hypothesis 2: The reduction in temperature after the candle extinguishes is responsible for the reduced air pressure. Prediction - if the temperature change is the sole cause of the change in pressure, we should expect to see no change in water level while the candle is burning (in the limit that the glass was lowered very slowly). After the burning stops, the water should rise at a rate related to the temperature drop and eventually stop as the experimental setup comes to room temperature.

In order to test which explaination is correct, you should be able to merely perform the experiment and match the observation with the prediction. Of course, in real life it may be a combination of these two factors or perhaps include other reasons not listed here. Additional measures such as putting an oxygen indicator in the glass (say a fresh slice of apple) or a thermometer would provide further insight. Good luck! linkimprove this answer

answered Jan 3 at 21:23

AdamRedwine 1,914114 1

As oxygen is burned - how many moles of CO2 do you get for each mole of O2 used? – Martin Beckett Jan 3 at 23:15

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@MartinBeckett: Not to mention it's mostly carbon monoxide because it's imperfect burning. – Mike Dunlavey Jan 4 at 3:15 @MartinBeckett: The pertinent equation seems to be something

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C25H52+38O2=>25CO2+26H2O. So for 1 mole of oxygen we have 0.65 moles of CO2 - a moderate reduction, and like

this assuming water condenses. – leonbloy Jan 4 at 14:40 @leonbloy - although with a smoky candle you do get a lot of CO. Plus since O2 is only 20% of air it would at most be a (10.65)*0.21 = 7% change in volume even with full combustion – Martin Beckett Jan 4 at 16:26 @MartinBeckett: you are right, of course. See the Harvard link in the other answer for the complete picture. – leonbloy Jan 4 at 16:36

I will make this into an answer because the idea behind this question is used in an ancient medical method which was still used by practical nurses and even prescribed by old fashioned doctors when I was a child more than half a century ago in Greece. It is now used in alternative medicine practices The air inside the cup is heated and the rim is then applied to the skin, forming an airtight seal. As the air inside the cup cools, it contracts, forming a partial vacuum and enabling the cup to suck the skin, pulling in soft tissue, and up vote 4 drawing blood to that area. down vote

I think it was the invention of antibiotics which diminished rapidly its use, which was mainly for bronchitis pneumonia and similar afflictions, at least in Greece. As far as the question goes, no liquids to confuse the issue of its being a strongly temperature dependent effect. linkimprove this answer

answered Jan 4 at

5:27

anna v 14.4k1925 Indeed, the practice is known as "cupping" and is often offered at spas and other health resorts. – AdamRedwine Jan 4 at 13:15 +1 In spanish: "ventosa". I've seen it applied by my grandmother many years ago. – leonbloy Jan 4 at 13:37 up vote answer is not oxygen its temperature change in the glass it cool rapidly which 0 down means it cools fast. DONE COPY ANSWER i dont know if its the right answer vote WARNING#1 DONT COPY DONT KNOW IF ITS THE RIGHT ANSWER i

did this experiencement 2 times.

Faraday's Candle In 1860 Michael Faraday gave the following series of Christmas Lectures at the Royal Instution of Great Britain, called "The Chemical History of a Candle": • •

Lecture I: A Candle: The Flame - Its Sources - Structure Mobility Brightness Lecture II: Brightness of The Flame - Air Necessary For Combustion Production of Water

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Lecture III: Products: Water From The Combustion - Nature of Water A Compound - Hydrogen

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Lecture IV: Hydrogen in The Candle - Burns Into Water - The Other Part of Water - Oxygen

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Lecture V: Oxygen Present in The Air - Nature of The Atmosphere Carbonic Acid

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Lecture VI: Carbon or Charcoal - Coal Gas - Respiration and Its Analogy to A Candle

You can read the lectures here.

They included 26 experiments, and among other things he showed how you could see the structure of a flame better by projecting its shadow on a wall. I tried this and here are the results. If you want to try this yourself, my tips are that bright sunlight works best for casting the shadow, and if you are going to photograph it, try reducing the exposure. If you see something you like, and would like to use or have a print of, email photos at subjectline dot co dot uk.