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How do you know whether a chemical reaction is exothermic or endothermic?

In an chemical reaction how do u know into what the reactant's change to which product???

  • I want to know if suppose a chemical reaction for eg:NaOH+HCl is given without any info on the product say the question is complate the following reaction.So what should the product be exactly? how do u kno?if thr is a certain method to follow please specify it.

  • Answer:

    The general answer is the products will minimize the "Gibb's Free Energy". Values for G can be looked up in tables and/or calculated for various pressures, concentrations, etc. So, if you can't look at the reaction and recognize it (like you can in this example) and it doesn't follow known rules (base+acid = salt+water), then you have to theorize different products (valid chemicals with the valances of each atom considered). Then grind out the deltaGs for each proposed reaction. If it is negative, it can happen with the right pathway. The biggest negative deltaG will be the preferred products. There are "delta G" reactors in computer-based reactor simulators (available in any Chemistry/ChemEng department at any college). It automatically spits out the % of each compound for the specified conditions. Some reactions are actually limited by kinetics (at normal pressures graphite is lower energy than diamond but it doesn't happen), but that is a different question

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Generally, an acid reacts with a base to form salt and water. For example NaOH + HCl --> NaCl + H2O This is known as nutralisation reaction.

dinu

yeah well if you read your gen chem text you'd find this stuff out. it's a double displacement reaction. here's the model AB+CD ---> AD +BC so applying that to your reaction NaOH + HCl ---> NaCl+ H2O it's also an acid base reaction where neutralization occurs. go back and review the basics.

shiara_blade

yes there are certain rules/methods.... this example is from the double displacement method. you juz basically exchange the partners hence: NaOH+HCl-->NaCl+H2O. there are other methods too such as the single replacement and watnot.. so juz go check your book or jzu check this out http://www.dbooth.net/mhs/chem/chemicalreactions.html

jaredkomahalko

based in ioinc charge and stibilty of the profict dived the reactants to + & - charge and swach beteen them

maherrashdan

normally i think they have indicators for indicating the completion of a reaction. like eg. phenolphthalein is added to determine if acid or base is fully neutralised not.. it takes more on knowledge and experiences.. hope this helps.. :)

smelly_ducks

hi. wellNaoh+ Hcl gives....Nacl +H2O SEE,IN ANY REACTION FIRST TRY TO SEPERATE OUT END PRODUCTS LIKE WATER OR ANY GAS.OK!THEN TRY TO MAKE COMBINATION OF LEFT SALTS....WHICH EXSISTS.OK!

Richa K

Rule of the thumb in chemical reactions is that, products formed should not be "stronger" than reactants consumed in such reaction. In your example of NaOH+HCl the product would be NaCl and H2O. Note however that the reverse of such reaction is not plausible, i.e. NaCl+H2O will not yield into NaOH and HCl. The reason behind this is that NaOH is a strong base while HCl is a strong acid. There are other factors you have to condiser when determining the possible products of a certain reaction. You also need to understand the type of chemical reaction to determine the possible products. In other words, there really is no easy way to determine what the products of chemical reactions would be. You need to have alot of experience with chemical reactions before you can determine the products of a reaction by merely looking at the left hand side of the chemical equation. Hope this helps. =)

Aris

Dinu---just gave you the correct answer. Now, give him 10 points.

~Jessica~

i don't know chemistry, i know physics

sixer

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