hermanntrude

of course there's a method. The trouble is that the laws of the universe do not permit us to re-make hydrocarbons for less energy than we get out of burning them. If it takes more energy to make hydrocarbons than we get from burning them (and it MUST... it's a law of thermodynamics) then there's no point in doing it.

the heats of formation are usually given in the question. If not, they're usually somewhere else in the resource you found the question in... for instance if it was a book, the heats are probably in a table or in an appendix.

the easiest method to reverse combustion is to be a plant. Plants take water and carbon dioxide and make sugars from them... sugars arent hydrocarbons but the plants also make a variety of hydrocarbons from the energy provided by the sugars

when a reaction is reversed, the sign of the enthalpy change is also reversed. What this means is that if a reaction gives a lot of energy out in the form of heat (like a combustion reaction does), then the reverse reaction requires that much energy to happen. Sometimes in reality it takes a lot MORE energy because of other factors too.

we could tell you, but that wouldnt really involve you doing your homework now, would it? what kinds of energy do you know about and how are they characterised? If you answer that question you've already answered your original question

an important addendum to this is that it's better not to even consider ANY kind of "diet" unless you are ACTUALLY OVERWEIGHT. Too many people think they're fat when they arent and try to lose weight uneccessarily, causing disappointment, depression and dangerous eating disorders.

seems to me trying to call light chiral is like trying to call a milk-carton a mammal because it produces milk.

welcome:) always nice to see someone with a genuine interest in chemistry. there's a few of us here. It sounds to me like you've learned about hybridisation and so on but not the crucial quantum mechanics behind it. Most textbooks have a chapter on basic quantum mechanics... it usually starts with the nature of waves, then proceeds to wave-particle duality, the photoelectric effect, then the Bohr atom and finally quantum mechanics. I figure you'd probably enjoy reading that chapter, especially if it's not covered in your chemistry course. I teach chemistry to two classes, the general class and the advanced class... the course for the general one doesnt include that chapter and it makes it SO much more difficult to teach the chapters afterwards, particularly the stuff involving hybridisation. I'm not sure about the description of hybridisation you give. It's not really about the promotion of an electron, but more about changing of the actual orbitals the electrons are "in". (electrons are often said to be "in" an orbital but electrons ARE the orbitals). The common example is when an "s" orbital is combined with three "p" orbitals to form four sp3 orbitals. The four new orbitals are all exactly the same energy as each other, where the s orbital was lower in energy than the p orbitals, so if there was an electron in the s orbital it was promoted to the sp3 orbital. However, if there were any electrons in any of the p orbitals, they were demoted to sp3. your question about manganese is a good one. However it's hard to answer quickly... manganese can form more oxidation states than most other elements, and ranges from totally ionic bonds to totally covalent bonds. It even forms [ce]Mn2O7[/ce] which is crazy stuff... why it does that is not so easy to explain.

cathode ray tubes arent hazard free... be careful. I'd give you some advice but i havent a clue how to build them. Remember, though that that beam of electrons is NOT entirely safe.

the 3d and 4s subshells are very close in energy so sometimes the order gets a bit confused. For instance, when adding electrons in the aufbau (building up) process, we say that the 4s subshell is filled before the 3d subshell. BUT when you come ionise a transition metal the electrons are lost from the 4s subshell first. Actually, though, it's more complicated than that. My advice is for you to wait until your course covers orbital hybridisation. This subject explains it all very nicely. However if you cant wait, try googling the topic.

on the wall in our main lecture theatre there is a PT with an f block containing 30 elements! i'm considering burning it

that's not what i suggested. It'd be much better if you could draw it first and then look it up afterwards to see if you got it right. Make sure you know how to draw Lewis structures. when you come to be tested you won't have google any more.

I think you're confused. The formula you used was for the mass/volume percentage, which is just one measure of concentration. The normal concentration unit to use is molarity, which is the moles of solute divided by litres of solution. You also applied your formula wrongly. The "m" is the mass of the solute. the "v" is the volume of solvent. An example would be if we dissolved 10g of NaCl in enough water to make a 100mL solution. m/v% would then be 10g/100mL *100% =10%. This measure of concentration is an unusual one usually only used in pharmaceuticals. As for the original question, i'm afraid i'm not sure if there's an equation.

i havent bought any yet. I think they're all fairly similar when you get the commercial ones.

there are periodic tables which place La and Ac in the f-block. There are others which place Lu and Lr in the f-block. Some do both. What do you know that the makers of these tables dont?

OK, i've been teaching this recently. Those are two absolute stinkers. However it might help you to know that they're similar to groups of sulfate ions stuck together. It's important to get the formulas of the ions before you start. After that, follow the rules: here's a simple method for drawing lewis structures, although it won't work for some of the harder species it should work for these ions. You might also want to try the tutorial application for sulfate ions here After that, if you still need more (which you might), try googling "thiosulfate ion" and "tetrathionate ion". You'll probably get pages with some lewis diagrams on them... you'll have to check to see if they're complete and correct and even if they aren't they'll help you to some extent. Post again if you're still having difficulties

Which blocks are these four elements in? I'm sure that some tables show La and Ac as being in the f-block and Lu and Lr in the d-block, whereas some put them all four in the f-block and some put Lu and Lr in the f-block and La and Ac in the d-block. It seems to me the whole mess of transition and inner-transition metals should be put in a d/f-block since there is so much mixing of electronic configurations.

amazon.com that's the american amazon, but i know the canadian and UK ones also used to sell it... they probably still do.

i'm fairly sure the temperature depends on several factors, including the design of the bunsen itself.

i'm not sure if there is a half equation for MnO4 in basic solution. if there is, I dont know it. As for your second question: something MUST be there, but it doesn't matter what it is. The only reason it's there is that the ions' charges must balance.

it's also very smart not to do this reaction and to at least partiallly understand what you're doing before you do it. It's also smart to recognise toxic nitrogen oxides when you see them. don't breathe that stuff, whatever you do!

Look at its electronic configuration. It SHOULD be paramagnetic. I havent a clue why, but when it's normally cooled (wihtout any fancy crystallisation) it's paramagnetic. Ive taken a peice which is paramagnetic, crystallised it, observed diamagnetism and then melted it again only to see the paramagnetism come back.

a thread is a particular topic, or subject. For instance, if you wanted to ask "what is laughing gas?" the best way to ask would be to go to the "general chemistry" forum and make a new thread with that title. Asking it in someone else's thread is considered bad manners.

rajesh, that's not the topic of this thread. Please don't hijack other people's threads

depends on the bunsen and the pressure of the gas. the ones in my lab reach about 700°C