Combining elements
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txteachers
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Combining elements
I was just wondering....is there a state of matter where any elements can be combined? Or do elements have to be in a certain state in order to combine with another element?
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agm
- Former Expert
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Re: Combining elements
Hi txteachers,
I can tell you a few things:
1. The state (or phase) of a material is a bulk property -- that is, it is defined by the collective arrangement of atoms within it. In the solid state, atoms stay in pretty much the same place relative to each other (for example, in a lattice arrangement), but they still wiggle around within little boxes due to thermal energy. In the liquid state, atoms are close to one another and interact strongly, but they are able to slither around easily -- think about what happens when you add a drop of food coloring to a glass of water -- so they don't maintain their relative positions for very long. In the gas phase, several atoms may be bound into a molecules, but molecules don't interact with each other very strongly with one another -- collisions are infrequent.
2a. The solid state: So, thinking about the above, if an atom "wanted" to react with one of its neighbors (if it was thermodynamically favorable to do so), usually this would happen when the atoms first came into contact as the material was being cooled. There aren't reactions going on in the interior of most solids, although I can't promise you that that could never happen -- the word of chemistry and materials is pretty diverse! It could be possible in some material that a reaction can occur below the melting temperature but above room temperature, so that if the material is cooled quickly, there isn't time for it to fully proceed. Then, if you heat that material slowly, that reaction could begin before it melts so that it happens in the solid state. You might find it interesting to read about annealing (though this isn't usually strictly a chemical process): http://en.wikipedia.org/wiki/Annealing_(metallurgy)
2b. Since an atom in the liquid state encounters new atoms frequently, reactions can easily occur here. However, if a liquid is kept at the same temperature for a long time without anything being added to it, all reactions that are thermodynamically favorable under those conditions will happen. (Often, reactions continue to proceed in both directions, but there is an equilibrium concentration of reactants and products when the forward and backward rates are equal, so there is no *net* reaction for the material.) But if you mix two liquids A and B together and molecules of A and B can react, they will certainly do so. Many reactions also happen between species dissolved in a solvent such as water.
2c. Atoms in the gas phase are certain mobile enough to encounter new atoms, but they do so less frequently than in liquids. However, some gases are highly reactive with one another when mixed. More info: http://chemed.chem.purdue.edu/genchem/t ... frame.html
3. A lot of reactions occur at interfaces between two phases. For example, rust can form when liquid water interacts with solid iron, and copper exposed to air acquires a patina over time: http://en.wikipedia.org/wiki/Patina. Because gas/liquid/solid phase is a bulk property, and the reaction occurs between individual atoms or molecules, this might be a more complicated situation than what you were thinking of.
4. A given reaction will occur at a rate (which can be so small that it's effectively zero) determined by temperature, pH, pressure, voltage, etc -- so it may be possible for it to occur in more than one phase. But this really depends on the particular reaction. I don't think there's a state where any possible reaction could occur, because all reactions have reverse reactions, and under most conditions (i.e. not the boundaries of phase diagrams) one or the other is significantly favored.
5. If you're asking whether for any two elements, there exist some conditions under which they would react to form a compound... I would guess probably not. In general, matter seeks the state of lowest energy, and reactions occur because the energy state achieved is lower (given the conditions). Combining certain elements would not result in a lower energy state. At higher temperatures, atoms are able to spend more time in higher-energy states, but they also tend to jump around between states very quickly. So at a very high temperature, you might see a "compound" that would normally never form, but it would only persist for an extremely small amount of time. Occasionally these configurations can be trapped by "quenching" (rapid cooling), but I doubt that is possible for every single compound you could conceive of. And at high enough temperatures, you get to the point where atoms are energetic enough to give up their electrons (plasma, the fourth state), and sharing of electrons is what creates chemical bonds, so you really can't talk about chemical reactions anymore.
Hope that helps,
Amanda
I can tell you a few things:
1. The state (or phase) of a material is a bulk property -- that is, it is defined by the collective arrangement of atoms within it. In the solid state, atoms stay in pretty much the same place relative to each other (for example, in a lattice arrangement), but they still wiggle around within little boxes due to thermal energy. In the liquid state, atoms are close to one another and interact strongly, but they are able to slither around easily -- think about what happens when you add a drop of food coloring to a glass of water -- so they don't maintain their relative positions for very long. In the gas phase, several atoms may be bound into a molecules, but molecules don't interact with each other very strongly with one another -- collisions are infrequent.
2a. The solid state: So, thinking about the above, if an atom "wanted" to react with one of its neighbors (if it was thermodynamically favorable to do so), usually this would happen when the atoms first came into contact as the material was being cooled. There aren't reactions going on in the interior of most solids, although I can't promise you that that could never happen -- the word of chemistry and materials is pretty diverse! It could be possible in some material that a reaction can occur below the melting temperature but above room temperature, so that if the material is cooled quickly, there isn't time for it to fully proceed. Then, if you heat that material slowly, that reaction could begin before it melts so that it happens in the solid state. You might find it interesting to read about annealing (though this isn't usually strictly a chemical process): http://en.wikipedia.org/wiki/Annealing_(metallurgy)
2b. Since an atom in the liquid state encounters new atoms frequently, reactions can easily occur here. However, if a liquid is kept at the same temperature for a long time without anything being added to it, all reactions that are thermodynamically favorable under those conditions will happen. (Often, reactions continue to proceed in both directions, but there is an equilibrium concentration of reactants and products when the forward and backward rates are equal, so there is no *net* reaction for the material.) But if you mix two liquids A and B together and molecules of A and B can react, they will certainly do so. Many reactions also happen between species dissolved in a solvent such as water.
2c. Atoms in the gas phase are certain mobile enough to encounter new atoms, but they do so less frequently than in liquids. However, some gases are highly reactive with one another when mixed. More info: http://chemed.chem.purdue.edu/genchem/t ... frame.html
3. A lot of reactions occur at interfaces between two phases. For example, rust can form when liquid water interacts with solid iron, and copper exposed to air acquires a patina over time: http://en.wikipedia.org/wiki/Patina. Because gas/liquid/solid phase is a bulk property, and the reaction occurs between individual atoms or molecules, this might be a more complicated situation than what you were thinking of.
4. A given reaction will occur at a rate (which can be so small that it's effectively zero) determined by temperature, pH, pressure, voltage, etc -- so it may be possible for it to occur in more than one phase. But this really depends on the particular reaction. I don't think there's a state where any possible reaction could occur, because all reactions have reverse reactions, and under most conditions (i.e. not the boundaries of phase diagrams) one or the other is significantly favored.
5. If you're asking whether for any two elements, there exist some conditions under which they would react to form a compound... I would guess probably not. In general, matter seeks the state of lowest energy, and reactions occur because the energy state achieved is lower (given the conditions). Combining certain elements would not result in a lower energy state. At higher temperatures, atoms are able to spend more time in higher-energy states, but they also tend to jump around between states very quickly. So at a very high temperature, you might see a "compound" that would normally never form, but it would only persist for an extremely small amount of time. Occasionally these configurations can be trapped by "quenching" (rapid cooling), but I doubt that is possible for every single compound you could conceive of. And at high enough temperatures, you get to the point where atoms are energetic enough to give up their electrons (plasma, the fourth state), and sharing of electrons is what creates chemical bonds, so you really can't talk about chemical reactions anymore.
Hope that helps,
Amanda