![]() You had propane here before, C3 H8, after the reaction you no You have chemical change, chemical change. And so what you actually have is the bonds in those molecules are actually breaking and then re forming. Moles of carbon dioxide gas and four moles of water Of molecular oxygen, you're gonna produce three Three for every one mole of propane and five moles And then when it combusts you're going to produce So for every mole of propane we have five moles of If you were to write theĬhemical reaction here it would be propane C3H8 in gas form. But if you have chemicalīonds forming or breaking that would be a chemical change. ![]() Intermolecular forces that tends to be a physical change. And we'll think about anĮdge case in a little bit is when you're overcoming When you think about what's going on on a microscopic level, and this is a general rule of thumb. Go from ice to water, physical change, from water to vapor or you could say from liquid to gas that is also going toīe a physical change. You have your intermolecularįorces being overcome but the covalent bonds between the oxygens and the hydrogens, those aren't breaking And if we kept heating that water up and it started to vaporize that would also be a physical change. And so you're not havingĪ change in composition. Each oxygen is stillīonded to two hydrogens. Now, we don't have aĬhange in composition, in either state whether you're looking at this liquid water here, or whether you're lookingĪt the solid water there, you'll see a bunch of water molecules. In fancy chemical language, or chemistry language, weĬould write this as H2O, going from its solid form to Think about this water, this ice melting. And I want you to think about which of these are physical changes, and which of these areĬhemical changes and why. We have some propaneĬombusting or burning here, and we have some iron rusting here. You is pause this video and we have some ice melting here. You actually do have a change in composition, how theĭifferent constituent atoms and elements match up orĬonnect or bond to each other might be different. Of what we're talking about, while in a chemical change Not having a change in the actual composition There could be a change in properties but we're But when we talk about a physical change, we're talking about where And you might already have already thought about this or seen this inĪ previous science class. And we're going to focus on in this video is classifying things asĮither being physical changes or chemical changes. ![]() Reversibility is not a distinction between the two since there are chemical changes which are reversible and nonreversible.Īre three different pictures of substances undergoing Chemical changes are when the identity of the chemicals change where we get new chemical with different properties. Physical changes are when just the structure of the matter changes, but not the chemicals. Solid salts are poor electrical conductors, while aqueous salt solutions are excellent electrical conductors. Solid salt and aqueous salt ions have different physical properties which would indicate that they are different chemicals and that a chemical change occurred. So the physical structure of the ions is changed, but the physical properties are also changed. If we heat the water so that it vaporizes, the ion-dipole bonds break and the ions are free to reform their previous ionic bonds. The dissolving, or dissolution, of a salt in water is considered a chemical change because we are breaking ionic bonds between the salt ions and forming new noncovalent ion-dipole bonds between the ions and the water molecules.
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