K.+Soo+Combustion+reaction.

=** Combustion Reaction. **=

[[image:propane1.jpg width="298" height="233" align="right"]]
In a combustion reaction, a substance combines with some form of oxygen to create one or more oxides, the products in a combustion reaction will usually be carbon dioxide and water.

** Formula. **
A + O2 —›  CO2 + H2O ...[combustion reactions generally look like this].

** Example of a combustion reaction. **
Propane (C3H8) combusts to yield carbon dioxide and water.

** Changing the word equation into a formula equation… **
The first thing that you need to do to change this word equation to a formula equation is to figure out the atomic symbols of the reaction’s reactants and products. It is given that propane is “C3H8”, “combusts” indicates that heat is added, meaning O2 (because oxygen is diatomic), carbon dioxide is CO2, and water is H2O. Write a formula equation using these atomic symbols: == C3H8 + O2 —›  CO2 + H2O The compounds are all correctly written because all the charges are neutral. Now balance the equation; go through the equation and figure out which elements are not equal on both sides of the equation. You can see that all the elements, carbon, hydrogen, and oxygen are all uneven. Start with hydrogen: on the left side, you can see that there are 8 hydrogen atoms but on the right, there is only 2. To have an equal number of hydrogens, you’ll need 8 on the right side as well so that it is balanced, and to do that, you have to put a coefficient of 4 before the product, H2O (so it will multiply the H2O to equal 8). C3H8 + O2 —› CO2 + 4 H2O Now that the hydrogen atoms are balanced, all that is left is the carbons and the oxygens. By adding the coefficient of 3 to the CO2, you end up with equal numbers of carbon atoms on both sides. C3H8 + O2 —› 3 CO2 + 4 H2O Now, all that remains unbalanced is the number of oxygens: there are now 10 oxygen atoms on the left (4 from the H2O added to 6 from the CO2) but only 2 on the left. To balance this, you need to end up with 10 oxygen atoms on the left as well. To do this, simply put a coefficient of 5 in front of the reactant O2 so that it will multiply to equal 10. C3H8 + 5 O2 —› 3 CO2 + 4 H2O The equation is finally balanced! When balancing equations, always remember that you can never change the subscripts, only coefficients.

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