Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: weedwhacker on January 20, 2010, 08:10:40 PM
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Hello everyone, I'm having trouble with predictions of reactions. A step-by-step guide on how to do these would be greatly appreciated! An example of the kind we're doing is Na(s) + H20(l) -->
We are covering several types of reactions including combustion, replacement, double replacement, synthesis and decomposition. Thanks in advance!
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Alkali metals and water always gives hydrogen gas and the hydroxide salt, i.e
2Na (s) + 2H2O (l) :rarrow: 2NaOH (aq) + H2 (g)
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Alkali metals and water always gives hydrogen gas and the hydroxide salt, i.e
2Na (s) + 2H2O (l) :rarrow: 2NaOH (aq) + H2 (g)
I see. So what exactly are the steps to solving these?
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There are no steps as such, it all comes with learning chemistry, these patterns you'll discover as you learn more. If you've got more questions, feel free to ask.
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Hi, I just registered on these forums and was just about to post a similiar queastion as the OP. So, i figured id post it in thsi chains.
(I was about to ask how can i know that water mixed whit hydrogen iodine makes iodine give its proton and not vica versa. How can I know this?)
These patterns you mentioned, do they apply to all chemistry?
From where can I learn these patterns?
"Alkali metals and water always gives hydrogen gas and the hydroxide salt"
"x mixed whit y always makes z happend"
...
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Okay, for your reaction here, let's break it down, firstly, HI, what is it? Well, under normal conditions it is a gas, how does one react a gas with water? The answer would be to bubble it through the water. But then what happens? Because the molecule is a small polar one, it will dissolve in water fairly easily
HI (g) + H2O (l) :rarrow: HI (aq)
Then, the next reaction is what you are talking about, the dissociation or 'breaking up' of the HI (aq). As you probably know, there are acids and bases, in the simplest case, an acid is a proton (H+) donor and a base is a proton acceptor. HI (aq) is a strong acid, meaning that it donates a proton readily, because the H-I bond is relatively weak (along with some other factors not to be worried about for the moment). Also, the bond formed between H2O and H+ is a stronger bond than an H-I bond, meaning that it releases more energy. SOME reactions occur in order to achieve minimum energy, in this case, this is one of them, because breaking the H-I bond requires less energy than is released when the O-H bond forms so overall, the system loses energy.
HI (aq) + H2O (l) :rarrow: H3O+ (aq) + I- (aq)
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So i just have to memorise how each chemical reacts whit another chemical? Isnt there a way to know this from the values of the atoms? Like from electronegativity
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As far as I am aware, no. Look, there isn't really that many reactions needed to be 'memorised' ::) but understanding 'why' it occurs is often better than 'how' cause then you can apply it to different situations rather than just any isolated reaction(s)
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Not really memorization, as much as knowing trends. How when Alkali/ Alkali Earth metals are reacted with "Hydrogen Oxide" "Dihydrogen Monoxide" "Hydro-Oxic Acid" "Hydrogen Hydroxide" or "Water" You get H2 gas and the hydroxide form of the metal