C3H8 + O2 –> H2O + CO2 This reaction occurs when propane (C3H8) is burned in the presence of oxygen to produce water and carbon dioxide.

For example, you have 3 oxygen atoms on the right side, but that total results from addition. Left side: 3 carbon (C3), 8 hydrogen (H8) and 2 oxygen (O2). Right side: 1 carbon (C), 2 hydrogen (H2) and 3 oxygen (O + O2).

You’ll need to recount your atoms before balancing the hydrogen and oxygen, as you’ll likely need to use coefficients to balance the other atoms in the equation.

C3H8 + O2 –> H2O + 3CO2 The coefficient 3 in front of carbon on the right side indicates 3 carbon atoms just as the subscript 3 on the left side indicates 3 carbon atoms. In a chemical equation, you can change coefficients, but you must never alter the subscripts.

C3H8 + O2 –> 4H2O + 3CO2 On the right side, you now added a 4 as the coefficient because the subscript showed that you already had 2 hydrogen atoms. When you multiply the coefficient 4 times by the subscript 2, you end up with 8.

Add a coefficient of 5 to the oxygen molecule on the left side of the equation. You now have 10 oxygen atoms on each side. C3H8 + 5O2 –> 4H2O + 3CO2. {“smallUrl”:“https://www. wikihow. com/images/thumb/6/63/Balance-Chemical-Equations-Step-7Bullet3-Version-2. jpg/v4-460px-Balance-Chemical-Equations-Step-7Bullet3-Version-2. jpg”,“bigUrl”:"/images/thumb/6/63/Balance-Chemical-Equations-Step-7Bullet3-Version-2. jpg/aid221334-v4-728px-Balance-Chemical-Equations-Step-7Bullet3-Version-2. jpg",“smallWidth”:460,“smallHeight”:345,“bigWidth”:728,“bigHeight”:546,“licensing”:"<div class="mw-parser-output">

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<br />\n</p></div>"} The carbon, hydrogen, and oxygen atoms are balanced. Your equation is complete. The other 6 atoms of oxygen come from 3CO2. (3x2=6 atoms of oxygen+ the other 4=10)

PCl5 + H2O –> H3PO4 + HCl

aPCl5 + bH2O –> cH3PO4 + dHCl

aPCl5 + bH2O –> cH3PO4 + dHCl On the left side, there are 2b atoms of hydrogen (2 for every molecule of H2O), while on the right side, there are 3c+d atoms of hydrogen (3 for every molecule of H3PO4 and 1 for every molecule of HCl). Since the number of atoms of hydrogen has to be equal on both sides, 2b must be equal to 3c+d. Do this for each element. P: a=c Cl: 5a=d H: 2b=3c+d

To quickly do this, take one variable and assign a value to it. Let’s make a = 1. Then start solving the system of equations to get the following values: Since P: a = c, we know that c = 1. Since Cl: 5a = d, we know that d = 5 Since H: 2b = 3c + d, we can calculate b like this: 2b = 3(1) + 5 2b = 3 + 5 2b = 8 b=4 This shows us the values are as follows: a = 1 b = 4 c = 1 d = 5 If the value you assigned returns fractional values, just multiply all values by the least common multiple (LCM) of the denominators to get rid of the fractions. If there is only one fraction, multiply all values by that values denominator. If the value you assigned returns coefficients that have a greatest common factor (GCF), simplify the chemical equation by dividing each value by the GCF.