How do you balance a chemical equation?

Answer 1

Before writing a chemical reaction, you must know a few things. You must know what the reactants are, and what the molecular formula of each one is. You must also know what the products of the reaction are, and how to write the molecular formulas for the products. Then you can go about writing the equation for the reaction and balancing the reaction.

In a chemical reaction, elements combine into compounds, compounds decompose back into elements, or transform existing compounds into new compounds. Because atoms are indestructible in chemical reactions, the same number of atoms of element must be present before and after any reaction. This is based on the principle of conservation of mass.

To balance a chemical equation, you must use stepwise reasoning. Sometimes there is some trial and error involved until you get enough practice to be good at it. It is something best learned with a lot of practice! The bottom line in any balanced reaction, and the way to test if you've done it correctly is this:

--HOWEVER MUCH OF ONE ELEMENT GOES IN, THE SAME AMOUNT MUST COME OUT!

Let's use this example: the decomposition of ammonium nitrate (NH4NO3) to dinitrogen oxide (N2O) and water (H2O). The unbalanced reaction is this:

NH4NO3 ---> N2O + H2O

On the LEFT side of the arrow are REACTANTS.

One the RIGHT side of the arrow are PRODUCTS.

Notice that the way the reaction is written not, 4 hydrogen atoms (H) go in, but only 2 come out (in the H2O) and also 3 oxygen atoms (O) go in as reactants, only 2 come out as products. This is NOT balanced! The nitrogen (N), by chance, does happen to be balanced: 2 go in as reactant, and 2 come out as products. To balance the reaction, we will add coefficients, or numbers, in front of certain reactants and products to make sure what goes in comes out!

First, assign 1 as the coefficient of one species (or compound or element), and usually you want to chose the most complicated compound containing the most elements. Here we should pick NH4NO3.

Secondly, find the elements that appear in only one other place in the equation, and assign coefficients to balance the numbers of their atoms. In our example, N appears in only one other place (N2O), and a coefficient of 1 for N2O ensures that for the 2 N's that go in, 2 come out. Hydrogen appears in H2O, and so its coefficient is 2 to balance the 4 H atoms on the left side. So now we have:

NH4NO3 ---> N2O + 2 H2O

Finally, check that the last element, O, is also balanced. In this case it is, as there are 3 on the left side and 3 on the right side. You don't need to put the "1" in front of the NH4NO3 and N2O. The number one is implied if you don't write a number.

Let's do it again for a different example, the burning of butane, C4H10, in oxygen gas (O2) to form carbon dioxide (CO2) and water (H2O). The unbalanced reaction is then

C4H10 + O2 -----> CO2 + H2O

Here is a good tip: leave blanks in front of each compound or element in the reaction so you have room to add the coefficients. Like this:

___ C4H10 + ___ O2 -----> ____ CO2 + ____ H2

Again, butane is the most complicated compound, so assign its coefficient to be one.

C4H10 + ___ O2 -----> ____ CO2 + ____ H2

Since there are 4 C's in butane, and the only place the C can go is into CO2, the coefficient in front of CO2 must be 4. In the same way, there are 10 H's in butane, and they can only go into the water, and so the coefficient in front of H2O must be 5 (10 H's divided by 2 H's per water).

C4H10 + ___ O2 -----> 4 CO2 + 5 H2O

Finally, we have to balance the oxygens. On the right we have 4*2 = 8 in the CO2, and 5*1 = 5 in the H2O, so that gives a total of 8+5 = 13. So now we have to make sure that 13 oxygen atoms are also on the left. Since we have O2 as the reactant, we can use a fraction as a coefficient to make the numbers come out right. Since we want 13 total, what number times 2 equals 13? That would be 13/2! So now we have:

C4H10 + 13/2 O2 -----> 4 CO2 + 5 H2O

Note that there is NOTHING WRONG WITH USING FRACTIONS in a balanced chemical equation. However, often people prefer to eliminate fractions because it makes it a bit easier to look at and work with. To do that, we simply multiply everything (on both side of the arrow) by 2:

2 C4H10 + 13 O2 -----> 8 CO2 + 10 H2O

--TO SUMMARIZE:

Sometimes you can balance a reaction by just looking at it and figuring it out very easily (it's called doing it "by inspection"). Other times it can be trickier and these steps can help.

--Step 1: Assign the number 1 as the coefficient to one species. Choose the most complicated one, with the most different elements in it.

--Step 2: Identify, one by one, elements that appear in only one species whose coefficient is not yet determined. Choose that coefficient to balance the number of atoms of that element. Continue until all coefficients are identified. Check to make sure that the number of atoms of each element on the left is equal to the number on the right of the arrow!

--Step 3: If you want (this is optional!), you can multiply the whole equation by the smallest integer that will get rid of any fractions.

Tricks:Sometimes it is difficult to balance an equation (non-combustion) with water in it and a hydroxide as a reactant. It is easier to write water as HOH (as opposed to H2O) so you can balance the hydroxide ions rather than the hydrogen and oxygen atoms solely.

HCl + Ca(OH)2 ---> CaCl2 + HOH

Take a look at the calcium hydroxide as a reactant. We know that there are two molecules of hydroxide, while there is only one as a product (may help to see it if you say H(OH) as a hydroxide molecule). So in the beginning, just balance the hydroxides, adding a "2" in front of the water molecule to bring a total of two hydroxide groups to balance the two from the reactant side. Then just balance the chlorine by adding a "2" in front of the hydrochloric acid.

2HCl + Ca(OH)2 ---> CaCl2 + 2HOH

Finally, you can count up all the individual hydrogen and oxygen atoms to make sure they are equal on both sides. This may seem like extra work, but it will actually simplify things and lets you balance more of the equation at once, rather than dealing with individual atoms. Formulas can become more complicated than this, and the HOH trick is a good one to have.

Answer 2

First need to either write down the equation if it's complete e.g.

PhCH3 + KMnO4 + H2SO4 = PhCOOH + K2SO4 + MnSO4 + H2O

or try to fill out an incomplete equation e.g. Ca(OH)2 + H3PO4 = ?

If you get this, try figuring out the products, for this equation, it would be Ca(OH)2 + H3PO4 = CaHPO4 + H2O

After writing down the complete symbol equation, you'll need to balance it.

Here's an example, MgBr2 + H2O = HBr + MgO This is an unbalanced equation. to balance it all sides of the reaction needs to be balance. we would see that in first part of the reaction, that there's 2 H and 2 Br (Br2) whereas, there's just 1 H and 1 Br, in the products, there's HBr, since we need 2 of both, put a 2 before it (2HBr). Since Mg and O is balanced on both sides, no need to balance it.

Here's the balance equation: MgBr2 + H2O = 2 HBr + MgO

So, in order to have a balanced equation, both sides of the equation have to be balanced.

---

To balance a chemical equation, you must add whole-number coefficients as needed before each substance until the number of atoms on the reactant side equals the number of atoms on the product side. For example, given the unbalanced equation: C3H8 + O2 --> CO2 + H2O, you must add whole-number coefficients to make it C3H8 + 5O2 --> 3CO2 + 4H2O to balance it. Things to remember: balancing a chemical equation means upholding the Law of Conservation of Mass, which states that matter cannot be created or destroyed; you can change coefficients, but not subscripts; coefficients are molar ratios; the absence of a coefficient means it's 1 (that applies to subscripts as well.)

Answer 3

1. Write the unbalanced equation.
   • Chemical formulas of reactants are listed on the lefthand side of the equation.
   • Products are listed on the righthand side of the equation.
   • Reactants and products are separated by putting an arrow between them to show the direction of the reaction. Reactions at equilibrium will have arrows facing both directions.
2. Balance the equation.
   • Apply the Law of Conservation of Mass to get the same number of atoms of every element on each side of the equation. Tip: Start by balancing an element that appears in only one reactant and product.
   • Once one element is balanced, proceed to balance another, and another, until all elements are balanced.
   • Balance chemical formulas by placing coefficients in front of them. Do not add subscripts, because this will change the formulas.
   • Use (g) for gaseous substances.
   • Use (s) for solids.
   • Use (l) for liquids.
   • Use (aq) for species in solution in water.
   • Write the state of matter immediately following the formula of the substance it describes.
3. Indicate the states of matter of the reactants and products.

HOPES THIS HELPS YOU A BIT !

Answer 4

balancing a chemical formula is somewhat easy to do if you know hot to solve it. take this chemical equation for example:

O2 + H3-> O + H3

This of course is very easy. You first check if the same number of atoms are on each side of the equation. This is not. There is 2 oxygen, 3 hydrogen on the reactants and 1 oxygen and 3 hydrogen on the product. The hydrogen is the same but the oxygen is not. one is a 2 while the other is a 1. you think to yourself "what can I multiply to 1 to get 2?" and you come up with 2. you then place it as a coefficient:

02 + H3 -> 2O +H3

Answer 5

The Chemistry equation is balanced with the law of conservation in mind which states that no atom can be destroyed or created in a given chemical reaction. To balance a chemistry equation the number of the atoms in the reactant side must be equal to the number of atoms in products side.

Answer 6

You figure out how many molecules of each reagent (on the left side) go in, and how many molecules of each product (on the right side) are produced, so that the total number of atoms of each element is the same on the two sides.

It's not so feasible to say exactly how to do that in a forum like this. (Even when I was teaching Chemistry, I used to teach this more by example than by giving rules. There aren't simple rules for how to turn a crank and get the answer.)

For example, when we burn methane (CH4) in air (using O2), we get water vapor (H2O) and Carbon Dioxide (CO2):

CH4 + O2 => H2O + CO2

This isn't balanced, (at least) b/c there are 4 H's on the left, and 2 on the right.

So the first thing we try is double the water:

CH4 + O2 => 2H2O + CO2

This still isn't balanced, b/c there are 2 O's on the left and 4 on the right, but the C and H are right. So we can double the Oxygen on the left, and then it all balances: Done! Everything adds up:

CH4 + 2O2 => 2H2O + CO2

Most people have to balance 10 - 30 equations before they can do it reliably. Just keep doing it, and it gets easier. Expect it to be a lot like banging your head against the wall the first few times, but believe me it gets much easier!

The one helpful rule I can give you is to start with the atoms that are only in the most complicated reagent, and end with the atoms that are only in the simplest reagent. That makes it easier.

Answer 7

All you have to do is find the number of atoms and do trial and error.