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39 votes
Accepted

How can there be decimal subscripts in a molecular formula?

First of all, in chemistry two types of formulas exist: structural and empirical. A structural formula shows the way atoms are connected. An empirical formula only summarizes atoms and their ratios. ...
permeakra's user avatar
  • 21.7k
24 votes

Why can't I balance this reaction algebraically?

Here's how to solve the system in python: ...
Curt F.'s user avatar
  • 22k
19 votes
Accepted

Why can't I balance this reaction algebraically?

Given the reaction $\ce{a Cu + b HNO3 -> c Cu(NO3)2 + d NO + e H2O}$, we can set up four equations: $$\begin{align} a &= c & &\text{(for Cu)} \tag{1} \\ b &= 2e & &\text{(...
MaxW's user avatar
  • 22.3k
19 votes

What is the mathematical meaning of the plus sign (+) in chemical reaction equations?

I think we are over-interpreting the poor $+$ sign. In older books you will also see an $=$ sign instead of an arrow just like what Lavoisier did. We have to get hold of La Traité Élémentaire de la ...
ACR's user avatar
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16 votes

What is the analogue of "molecule" for ionic compounds?

The term you are looking for is formula unit, I think. Wikipedia doesn't really describe it super well, but just to give an example, you could write the sentence $\pu{58.44 g}$ of $\ce{NaCl}$ ...
orthocresol's user avatar
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15 votes

Can a chemical reaction have two balanced equations?

You can expand the second equation so it has the same amount of educt on the left side as the first one: $$\ce{6XeF4 + 12H2O → 3Xe + 3XeO3 + 24HF + 1.5 O2}$$ Difference on the product side, compared ...
Karl's user avatar
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14 votes

What's the difference between reactant, excess reactant and limited reactant in a balanced equation?

Suppose that you want to make a cake. You would first need to go your fridge to check whether you have the necessary ingredients to make one. So you go to your fridge. Luckily, you have all the ...
CoffeeIsLife's user avatar
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14 votes
Accepted

Are chemical equations like a cooking recipe?

Cooking and baking each involve a lot of chemistry themselves, and this analogy largely holds in the case of stoichiometry. One might take liberty with a cooking or baking recipe and change it, adapt ...
thelocalsage's user avatar
  • 1,247
13 votes

Unknown notation relating to stoichiometry

It is probably supposed to be the 'corresponds to' sign[ref, p 105]; in this case simply representing that for every two moles of $\ce{NaOH}$ one mole of $\ce{H2SO4}$ is converted by reaction ...
Linear Christmas's user avatar
13 votes
Accepted

What does n(Na2CO3) mean?

Yes, the standardized quantity symbol according to ISO 80000-9:2009 Quantities and units — Part 9: Physical chemistry and molecular physics as well as the recommended quantity symbol according to ...
Loong's user avatar
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12 votes
Accepted

Unknown notation relating to stoichiometry

The sign $≏$ is read "is chemically equivalent to". The term chemically equivalent refers to a specific chemical reaction. For the reaction $$\ce{N2(g) + 3 H2(g) -> 2NH3(g)}$$ $$\pu{1 mol } \ce{N2} ...
Apoorv Potnis's user avatar
11 votes

What is an equivalent?

Equivalent concept is an archaic unit of measurement that was used in chemistry and the biological sciences in the era before researchers knew how to determine the chemical formula for a compound. An ...
Tushar's user avatar
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11 votes

More than one way of balancing a chemical equation

This happens when you have a sum of two (or more) independent reactions. You can balance each one, and then add them together in an arbitrary proportion. People usually run into this when trying to ...
Ivan Neretin's user avatar
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11 votes

What is the mathematical meaning of the plus sign (+) in chemical reaction equations?

Here is an interpretation I came up for it, so suppose you have the molecule $\ce{CH4}$, then we can think of this as a vector as $ \langle 1,4 \rangle$ where the $1$ stands for number of carbons and $...
Cathartic Encephalopathy's user avatar
11 votes

Does stoichiometric gas mixture produce the highest explosion pressure (or energy) compared with other explosive limit mixture?

Yes, the stoichiometric mixture is the most energetic and creates the highest pressure. If the mix is not stoichiometric, then some of the energy of the explosion goes into heating up and expanding ...
Curt F.'s user avatar
  • 22k
10 votes
Accepted

Balancing the reaction equation for the oxidation of lead(II) sulfide with ozone

This is a semi-standard example of why 'naive' balancing does not work. Ozone is a source of atomic oxygen, producing free oxygen molecules. So, in 'mild' conditions only one oxygen per ozone ...
permeakra's user avatar
  • 21.7k
10 votes

What is the difference between ''1 C atom and 1 mole of C atoms?''

What is the difference between one egg and one dozen eggs? A dozen is simply a certain count, in this case 12, that is rendered as one unit for our convenience. Avogadro's number s just the same ...
Oscar Lanzi's user avatar
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10 votes

Balancing reaction between copper and nitric acid given the ratio of formed nitrogen oxides

The final arbiter of formal correctness of chemical reaction enumeration are laws of mass and charge conservation. If total counts of charge and atoms of every element are not the same on each side, ...
Poutnik's user avatar
  • 42.7k
9 votes

Why can't I balance this reaction algebraically?

You seem to have had the right idea of fixing the scale by arbitrarily choosing the value of one coefficient, and then solving for the rest. Apparently, you just got stuck at some point, presumably ...
Ilmari Karonen's user avatar
9 votes
Accepted

How is the the law of chemical equivalence defined and what are its limitations?

Basically the law of equivalence wants you to balance the equivalents that are involved in your reaction. I'd like you to view you reactions in two parts, the oxidation and reduction halves. I see: $$...
Berry Holmes's user avatar
  • 4,174
9 votes

Unknown notation relating to stoichiometry

I suppose it's a $\Large ≏$ "difference between" math symbol, which here denotes inequality in amounts between acid and base. Can be typed using $\rm \LaTeX$ command ...
andselisk's user avatar
  • 38.4k
9 votes
Accepted

Is it possible for me to derive Avogadro's number?

To determine Avogadro's number you have to measure the same unit at the atomic and macroscopic scales. This was first achieved by Millikan who measured the charge of an electron. The charge of one ...
Raoul Kessels's user avatar
9 votes

Net production of CO2 in plants

Plants are able to store energy as carbohydrates, i.e. they can make more carbohydrates than they need for their metabolism when there is no sunlight, and store it for later use. So the amount of ...
imalipusram's user avatar
9 votes

What is the mathematical meaning of the plus sign (+) in chemical reaction equations?

Answer is no, there is no strict mathematical interpretation. We can say that 1 mol of methane reacts with 2 moles of oxygen, but that is hardly any kind of mathematical interpretation. Plus sign only ...
Dario Mirić's user avatar
8 votes
Accepted

What happens when potassium iodide is added to a copper (II) salt?

When writing a reaction, you should take care to keep charges and atoms balanced. So the very first reaction you postulated is good (it has charges and atoms balanced) but then it goes South. If you ...
Jan's user avatar
  • 68.4k
8 votes
Accepted

Why does multipying a scalar in both sides of a balanced chemical equation, change related quantities?

Maybe because the equilibrium constant, Gibbs energy, enthalpy, etc. are not the fundamental characteristics you think they are. Really, what does enthalpy mean, for example? Say, a reaction $\ce{A + ...
Ivan Neretin's user avatar
  • 31.3k
8 votes
Accepted

Balancing the equation

First balance the number of atoms both side (except H and O). $$ \ce{Cr2O7^2- -> 2 Cr^3+} $$ Since the oxidation number of Cr on the left is $+ 6$ while on the right, it is $+ 3$, since 2 atoms of ...
Vidyanshu Mishra's user avatar
8 votes
Accepted

Law of mass action & Collision Theory

The law of mass action only rigorously applies to elementary reactions (in that otherwise the exponents do not match stoichiometric coefficients). These are reactions whose equations match which ...
Linear Christmas's user avatar
8 votes
Accepted

Calculate the number of atoms of oxygen present in 1.3 mol of sulfuric acid

The key about the unit mole is that it does not reference which type of entity is specified. Using the mole only makes sense if you define what you are using the mole for. This could be: protons ...
Jan's user avatar
  • 68.4k
8 votes
Accepted

Finding average Mr of a gaseous mixture

I suspect one might utilize the fact that all three compounds – cyclohexanol $\ce{C6H12O}$, acetone $\ce{C3H6O}$ and pentanal $\ce{C5H10O}$ – share the same empirical formula $\ce{(CH2)_xO}$, which is ...
andselisk's user avatar
  • 38.4k

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