How do you balance this equation: #?C_5H_12 + ?O_2 → ?CO_2 + ?H_2O + heat#?

2 Answers
anor277
Mar 6, 2017

#C_5H_12 + 8O_2 rarr 5CO_2 +6H_2O + Delta#

Explanation:

Well is it stoichiometrically balanced? Garbage out must equal garbage in if it is to be a proper representation of chemical reality. And not only is it balanced with respect to mass and charge, it is also balanced in terms of energy transfer. A given quantity of pentane results in a precise quantity of energy upon complete combustion.

As to how to do it, the usual rigmarole is to:

#(i)# #"Balance the carbons as carbon dioxide"#

#(ii)# #"Then balance the hydrogens as water"#

#(iii)# #"And then balance the oxygens on the LHS".#

See here for another example.

Meave60
Mar 6, 2017
  1. Balance the carbon atoms.
  2. Balance the hydrogen atoms.
  3. Balance the oxygen atoms.

#"C"_5"H"_12 + color(purple)("8")"O"_2##rarr##color(red)("5")"CO"_2 + color(green)("6")"H"_2"O" + "heat"#

Explanation:

Balance the equation:

#"C"_5"H"_12 + "O"_2##rarr##"CO"_2 + "H"_2"O" + "heat"#

Due to the law of conservation of mass/matter , the number of atoms for each element must be the same on both sides. When balancing a chemical equation, the chemical formulas are never changed , which means subscripts are never changed. What can change is the amount of each reactant and product. The amount is indicated by a coefficient in front of a formula. The coefficient is multiplied by the subscripts of the elements in the formula.

The strategy for balancing combustion reactions is:

  1. Balance the carbon atoms.
  2. Balance the hydrogen atoms.
  3. Balance the oxygen atoms.

Carbon and Hydrogen

There are 5 C atoms on the left and 1 C atom on the right. Place a coefficient of #5# in front of the #"CO"_2#. There are 12 H atoms on the left side, and 2 H atoms on the right. Place a coefficient of #6# in front of the #"H"_2"O"#.

#"C"_5"H"_12 + "O"_2##rarr##color(red)("5")"CO"_2 + color(green)("6")"H"_2"O" + "heat"#

Oxygen

There are 2 O atoms on the left and 16 O atoms on the right. Place a coefficient of #8# in front of the #"O"_2"#.

#"C"_5"H"_12 + color(purple)("8")"O"_2##rarr##color(red)("5")"CO"_2 + color(green)("6")"H"_2"O" + "heat"#

Check the numbers of atoms of each element on each side.

Left Side: #"5 C atoms"#, #"12 H atoms"#, #"16 O atoms"#

Right Side: #"5 C atoms"#, #"12 H atoms"#, #"16 O atoms"#

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