Yttrium2
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why do these ignite?
Yttrium turnings in air
Or a lit match igniting gasoline
How do each of these ignite, and what happens at the atomic/molecular level that creates ignition, and flame
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Loptr
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Oxidation + Reduction
Heat is a catalyst in a lot of cases, and catalyzes the oxidation of a material.
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Yttrium2
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Why doesn't steel wool burn in the air through oxidation reduction?
Where does it say how hot it needs to be for oxidation to happen
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Molecular Manipulations
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Steel wool does burn in air. Where do you get your' information?
Oxidation-reduction happens at all temperatures. Kinetics make it very slow at low temperatures which prevents a "run-away" reaction. When something
is burning, it's reached a temperature that allows the heat produced to keep the reaction going fast enough to continue the reaction until the
limiting reactant is depleted.
All of the questions you've been asking are very simple and can be found within seconds online.
-The manipulator
We are all here on earth to help others; what on earth the others are here for I don't know. -W. H. Auden
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Loptr
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(I am a bit rusty so correct me if I am wrong)
The burning of steel wool produces FeO, or iron(ii) oxide, correct? So check to see what the heat of formation is for that compound. It's a question
of enthalpy and thermodynamics.
Also, steel wool burns only slowly in air, which is about 20% oxygen. Put it in 100% and it burns pretty easily and quickly!
http://chemwiki.ucdavis.edu/Physical_Chemistry/Thermodynamic...
[Edited on 19-3-2015 by Loptr]
By the way, I love this video by NightHawkInLight.
Steel Wool Fireworks on the Beach
https://www.youtube.com/watch?v=gnRcDtMniVE
* Steel wool burning in air. You see it accelerate in burning as he swings it, and that is because it is being subjected to more oxygen than it would
be if at rest.
[Edited on 19-3-2015 by Loptr]
More steel wool in oxygen.
https://www.youtube.com/watch?v=TkE1uVjrY0w
[Edited on 19-3-2015 by Loptr]
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Loptr
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Quote: Originally posted by Molecular Manipulations  | Steel wool does burn in air. Where do you get your' information?
Oxidation-reduction happens at all temperatures. Kinetics make it very slow at low temperatures which prevents a "run-away" reaction. When something
is burning, it's reached a temperature that allows the heat produced to keep the reaction going fast enough to continue the reaction until the
limiting reactant is depleted.
All of the questions you've been asking are very simple and can be found within seconds online. |
I think the OP meant simply bursting into flames by being oxidized by oxygen in the air, or at least that is how I interpreted the post.
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jock88
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Also it depends how fine the steel wool is.
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Loptr
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Iron with a very large surface area can be pyrophoric in air. I believe that if you decompose iron oxalate you end up with nano-sized iron particles,
that if dropped through the air off the end of a spatula, will indeed catch on fire on the way down without a heat source.
[Edited on 19-3-2015 by Loptr]
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Molecular Manipulations
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| Quote: Originally posted by Loptr |
if you decompose iron oxalate you end up with nano-sized iron particles, that if dropped through the air off the end of a spatula, will indeed catch
on fire on the way down without a heat source. |
Yeah, I've done this demonstration several times. Heat iron oxalate in a test tube with a bunsen burner until gas evolution stops. Then tip the tube
upside down. As the pyrophoric black iron powder falls it ignites, really fun demo!
When heated, iron oxalate dehydrates and decomposes into carbon dioxide, carbon monoxide, iron oxides and pyrophoric black iron.
-The manipulator
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Metacelsus
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Normally I'm not this pedantic, but there is an important distinction to be made. Heat supplies activation energy for the reaction. It does not act as
a catalyst.
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Yttrium2
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The answer about heat of formation was kind of what I was looking for, could someone explains exactly how it applies to the questions scenario.
However, I did enjoy reading the rest.
[Edited on 19-3-2015 by Yttrium2]
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Loptr
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| Quote: Originally posted by Cheddite Cheese |
Normally I'm not this pedantic, but there is an important distinction to be made. Heat supplies activation energy for the reaction. It does not act as
a catalyst. |
A particular reaction pathway will have a needed activation energy. Heat provides a higher temperature, and therefore atoms and molecules involved
have higher energy than without it. As you know, a catalyst is a chemical agent that modifies the reaction pathway to one of a lower activation
energy, but doesn't participate in the actual reaction and end up on the product side. While heat may not be a catalyst purely in a chemical sense, it
does catalyze the reaction by providing the required activation energy--semantics or an error in my causal relationship.
Correction: Heat provides energy towards the needed activation energy, and is not an actual catalyst in the chemical sense of the word.
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Molecular Manipulations
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In equilibrium heat is considered a reactant or product. Acc. Le Châtelier's principle the equilibrium constant will shift under "stress", if you add
a reactant, the equilibrium will shift to make more product - and vise versa. Since heat, or energy is considered either a product or reactant
(corresponding to an exothermic or endothermic reaction respectively) adding energy to a exothermic reaction (eg. burning steel wool) will cause the
reverse reaction to occur more than it otherwise would. Now of course in the case of highly exothermic reactions, the Heat of Formation will insure
that the reaction goes practically to completion, even when heat is added - just slightly less than otherwise.
Heat of Formation is the amount of energy released when a mole of the substance is formed from its' elements. It's path independent, meaning it
doesn't matter how the products are formed, the same amount of energy will be released regardless of the path.
Activation energy is the energy required to break the reactants' bonds in order to allow the products to form via formation of stronger bonds. In
diatomic gasses the bonds must break to form new bonds. The amount of energy needed to break a specific bone can be calculated: H2 → 2
H· ΔG = 102 kcal/mol
Cl2 → 2 Cl· ΔG = 58 kcal/mol
Br2 → 2 Br· ΔG = 46 kcal/mol
I2 → 2 I· ΔG = 36 kcal/mol
The color of these gasses is actually because of their dissociation, which occurs automatically. That's why each halogen gets darker in color as they
go down the row, their dissociation energy gets smaller and so iodine dissociates more than bromine etc.
-The manipulator
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Loptr
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| Quote: Originally posted by Molecular Manipulations | In equilibrium heat is considered a reactant or product. Acc. Le Châtelier's principle the equilibrium constant will shift under "stress", if you add
a reactant, the equilibrium will shift to make more product - and vise versa. Since heat, or energy is considered either a product or reactant
(corresponding to an exothermic or endothermic reaction respectively) adding energy to a exothermic reaction (eg. burning steel wool) will cause the
reverse reaction to occur more than it otherwise would. Now of course in the case of highly exothermic reactions, the Heat of Formation will insure
that the reaction goes practically to completion, even when heat is added - just slightly less than otherwise.
Heat of Formation is the amount of energy released when a mole of the substance is formed from its' elements. It's path independent, meaning it
doesn't matter how the products are formed, the same amount of energy will be released regardless of the path.
Activation energy is the energy required to break the reactants' bonds in order to allow the products to form via formation of stronger bonds. In
diatomic gasses the bonds must break to form new bonds. The amount of energy needed to break a specific bone can be calculated: H2 → 2
H· ΔG = 102 kcal/mol
Cl2 → 2 Cl· ΔG = 58 kcal/mol
Br2 → 2 Br· ΔG = 46 kcal/mol
I2 → 2 I· ΔG = 36 kcal/mol
The color of these gasses is actually because of their dissociation, which occurs automatically. That's why each halogen gets darker in color as they
go down the row, their dissociation energy gets smaller and so iodine dissociates more than bromine etc. |
It was my understanding that the heat of formation is is a measure of the energy released or consumed when one mole of a substance is created under
standard conditions from its pure elements. I am not sure what doesn't constitute standard conditions. Perhaps non-atmospheric pressure?
I also didn't know that activation energy was specific to breaking bonds in order to allow the products to form. I thought it was a more general
concept than that, and was more of a minimum amount of energy needed in order to start a chemical reaction. Such as with Greek mythology and Sisyphus,
I thought the activation energy is the amount of energy that must be provided in order for the stone to make it over the mountain, and the stone
rolling down the other side of the mountain is the chemical reaction.
[Edited on 20-3-2015 by Loptr]
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DraconicAcid
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| Quote: Originally posted by Molecular Manipulations | | In equilibrium heat is considered a reactant or product. Acc. Le Châtelier's principle the equilibrium constant will shift under "stress", if you add
a reactant, the equilibrium will shift to make more product - and vise versa. Since heat, or energy is considered either a product or reactant
(corresponding to an exothermic or endothermic reaction respectively) adding energy to a exothermic reaction (eg. burning steel wool) will cause the
reverse reaction to occur more than it otherwise would. |
That's a big simplification. The rate of a reaction will depend on its activation energy and the temperature (which determines the fraction of
collisions which will have sufficient energy to reach the transition state). Increasing the temperature will increase the rate of any reaction, but
the effect is greater on a reaction with a higher activation energy. For an exothermic reaction, the activation energy for the reverse reaction is
larger than that of the forwards reaction, so the reverse reaction is accelerated more (this decreases the equilibrium constant, which can be derived
as a ratio of the forwards and reverse rate constants).
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Molecular Manipulations
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Loptr Standard conditions is 0 °C and 100 kPa (1 bar).
Yeah, activation energy is breaking specific bonds.
DraconicAcid My simplification had nothing to do with rates of reaction, only equilibrium.
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