CHEMISTRY COMMUNITY

When balancing an equation in lecture prof Lavelle multiplied the entire equation by 2 in order to get the lowest whole number. Will points be deducted on the test if we don’t do so ?

In lecture, Dr. Lavelle said that all stoichiometric coefficients must be the lowest whole number, so I imagine you would be docked points for leaving any coefficients in fractions.

You most likely would be deducted points since stoichiometric coefficients must be the lowest whole number

I remember him saying that the ratios still make sense despite it not being a whole number. However for the sake of nature, I suppose, it is important to keep it at the lowest whole number to get your empirical/ molecular formula to get points on it on an exam.

I would keep everything at whole numbers just to be safe. I haven't seen any chemical equations that have decimals or fractions as the stoichiometric coefficient.

How are we supposed to know what number to multiply by in order to attain whole integers? Knowing if we need to multiply by 2 or 3 to reach a whole number is easy, but what about when the solution is more complicated?

An easy way for me to determine what number to multiple a decimal by to get a whole number is to divide 1 by the decimal.

For example:
If there are 2.5 mols of C, do 1/0.5 = 2. You should multiply the 2.5 mols by 2 to get a whole number (5).
If it's a more difficult value, maybe like 2.125 mols of C, do 1/0.125 = 8. You would then multiply the 2.125 mole by 8 to get a whole number (17).

When you need to use a stoichiometric coefficient that is not a whole number, you can write it as an improper fraction (such as 5/4). Then you will know to multiply the whole equation by the denominator (in this case 4) to get the lowest whole number.

Conventionally the stoichiometric coefficients are whole numbers as it makes stoichiometric calculations more straightforward. Having whole numbers will make it easier to find out how many moles of Product A can be theoretically produced with x amount of moles of reactant B. It would be strange to say "if we have 6.5 moles of butane, we can produce 13.25 moles of H20" (arbitrary values) rather than "2 moles of butane can produce 8 moles of water given sufficient oxygen molecules" (again, arbitrary values). As the others have stated, I would most definitely make sure that the coefficients are whole numbers as it is the convention in every chemistry textbook that I have seen.

alicechien_1I wrote:An easy way for me to determine what number to multiple a decimal by to get a whole number is to divide 1 by the decimal.

For example:
If there are 2.5 mols of C, do 1/0.5 = 2. You should multiply the 2.5 mols by 2 to get a whole number (5).
If it's a more difficult value, maybe like 2.125 mols of C, do 1/0.125 = 8. You would then multiply the 2.125 mole by 8 to get a whole number (17).

Huh, this is actually awesome. In the past, I've always used my intuition to make educated guesses about the correct factor, but this completely takes the uncertainty out of the equation. Can't believe I didn't think to try this myself and thank you so much for your post!

You would probably lose points. Also even though the equation is balanced without whole numbers, it doesn't make sense for there to be half of a molecule. It would not only make more sense but also make solving problems later on easier with whole number coefficients.

alicechien_1I wrote:An easy way for me to determine what number to multiple a decimal by to get a whole number is to divide 1 by the decimal.

For example:
If there are 2.5 mols of C, do 1/0.5 = 2. You should multiply the 2.5 mols by 2 to get a whole number (5).
If it's a more difficult value, maybe like 2.125 mols of C, do 1/0.125 = 8. You would then multiply the 2.125 mole by 8 to get a whole number (17).

This is a really interesting way of figuring out how to find whole number coefficients. Although, based on the example in class Lavelle used fractions, decimals for balancing chemical equations makes logical sense as well. Also, don't forget to find the simplest ratio of all the whole number coefficients at the end of balancing each chemical equation.

alicechien_1I wrote:An easy way for me to determine what number to multiple a decimal by to get a whole number is to divide 1 by the decimal.

For example:
If there are 2.5 mols of C, do 1/0.5 = 2. You should multiply the 2.5 mols by 2 to get a whole number (5).
If it's a more difficult value, maybe like 2.125 mols of C, do 1/0.125 = 8. You would then multiply the 2.125 mole by 8 to get a whole number (17).

Thank you for this! I usually just try to make an educated guess, but this is a better approach and I will definitely be using it. Also, as a follow up question to the original question, do the coefficient have to be the lowest possible or is it okay to have bigger numbers as long as the ratios are the same?

All stoichiometric coefficients must be the lowest whole number, and multiplying by 2 would give the lowest whole number coefficients for that equation!

I'm pretty sure most of the time when you balance chemical equations, you will not need to use fractions as stoichiometric coefficients. So I'd say for the most part don't worry about it, just make sure the coefficients are ALWAYS whole numbers. You may not run into many problems with fraction coefficients though.

Yes! All coefficients should be put to the lowest whole number! I am not exactly sure if you will be deducted though.

I think I can confidently say yes, since stoichiometric coefficients must be whole numbers.

If leaving the coefficients in fractions when solving for them is helpful, then do that first. After you balance the equation, you can just multiply all the coefficients by the common denominator for the fractional stoichiometric coefficients.

If leaving the coefficients in fractions when solving for them is helpful, then do that first. After you balance the equation, you can just multiply all the coefficients by the common denominator for the fractional stoichiometric coefficients.

gabbymaraziti wrote:How are we supposed to know what number to multiply by in order to attain whole integers? Knowing if we need to multiply by 2 or 3 to reach a whole number is easy, but what about when the solution is more complicated?

normally, the numbers should be pretty easy fractions, but if they turn out a little messy I would probably check the previous compounds that I have balanced, as an error in those balances may affect the math later on

When balancing equations how do you determine what to balance first?

duenezjuleny1D wrote:When balancing an equation in lecture prof Lavelle multiplied the entire equation by 2 in order to get the lowest whole number. Will points be deducted on the test if we don’t do so ?

I would assume you'd receive a lower grade if you didn't do something similar, because if you recall, in the example, he did that so that the subscript in the equation was a whole number. You can't submit a final equation with a fraction of an atom in it, so you should always multiply the whole thing by whatever number it requires to make it a whole number before submitting a final answer.

Debora Fernandez Clemente_ 4H wrote:When balancing equations how do you determine what to balance first?

My TA recommended that we start with balancing the elements that appear the least in a chemical equation.
For example:
You would start with either the Carbons or Hydrogens since they each only appear twice throughout the entire chemical equation whereas the Oxygen appears three times.

The stoichiometric coefficients in chemical equations must always be the lowest integer (whole number). In the example he gave in class, Prof. Lavelle multiplied the equation by two to get rid of the fraction. What he was left with were the lowest whole numbers possible. I don't think you are supposed to leave fractions in a chemical equation when balancing it. Always find the lowest possible whole numbers (even if it means having to multiple to not have fractions).

That was definitely a technique he used for that specific problem! Working with stoichiometry problems will never have the same set of moves for each problem. In this case, we had a coefficient with a denominator of 2, so we had to multiply the entire problem by 2 in order to get rid of the fraction. If there was a coefficient of lets say 1/3, you might consider multiplying the whole equation by 3 (but again, each problem has its own way of getting solved, or potentially multiple strategies).

duenezjuleny1D wrote:When balancing an equation in lecture prof Lavelle multiplied the entire equation by 2 in order to get the lowest whole number. Will points be deducted on the test if we don’t do so ?

The reason why we want all coefficients to be whole numbers is because we are trying to find the mol to mol ratio between reactants and products in a chemical reaction, and it's easier to work with whole numbers.