Carbon dioxide is produced when a fuel burns completely. Its formula is CO2. A student writes 3CO2 to represent three molecules. How many oxygen atoms in to...
Question 1 Report
Carbon dioxide is produced when a fuel burns completely. Its formula is CO2. A student writes 3CO2 to represent three molecules. How many oxygen atoms in total are represented by 3CO2?
Answer Details
A large number written in front of a formula multiplies the whole formula, while a subscript applies only to the atom it follows. In 3CO2 the subscript 2 gives two oxygen atoms per molecule and the 3 in front means three such molecules, so the oxygen total is \(3 \times 2 = 6\) atoms. There are also \(3 \times 1 = 3\) carbon atoms.
Answering 3 counts the molecules rather than the oxygen atoms, and answering 2 ignores the multiplier and counts a single molecule. An answer of 5 comes from adding \(3 + 2\) instead of multiplying. This distinction between the large number in front and the small subscript is exactly what makes equation balancing work, because only the front number may be changed when balancing.
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