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### Balancing Chemical Equations Online Module Assessment

Posted: Tue Apr 10, 2018 5:17 pm

19. During a summer camping weekend 4 moles of butane (C4H10) gas were used for cooking. Chose the right balanced equation for the combustion of 4 moles of butane gas. What is the net number of moles of gas produced?

A. 4C4H10(g) + 26O2(g) → 16CO2(g) + 20H2O(g); 6

B. 4C4H10(g) + 26O2(g) → 16CO2(g) + 18H2O(g); 4

C. 4C4H10(g) + 25O2(g) → 16CO2(g) + 20H2O(g); 6

D. 4C4H10(g) + 26O2(g) → 16CO2(g) + 20H2O(g); 5

The correct answer is A, which I chose. I understand how to balance the equation and how to find the net number of moles produced [(moles of product)-(moles of reactant)]. However, I remember Dr. Lavelle mentioning the conservation of mass in chemical reactions and how the amount of moles on the left must equal the amount of moles on the right. Following this logic, why would there be a net number of moles since the number of moles of each element must be the same on both sides? Thanks in advance! :)

### Re: Balancing Chemical Equations Online Module Assessment

Posted: Wed Apr 11, 2018 12:36 am
The amount of moles of each compound are actually not the same because they represent the molar ratios, in other words, the coefficients. The purpose of balancing chemical equations is to make sure you have the same number of elements on both sides. In the example, there are 16 carbons on the left and 16 carbons on the right. You are not looking for equal amounts of moles, but you are looking equal amounts of mass. 16 carbons have the same mass as another 16 carbons. This where the Law of Conservation of Mass comes into play. As long as the mass of the element carbon is equal on both sides, the molar ratios do not matter. Molar ratios just represent how many moles of one compound are needed to be equivalent to another compound. I hope this helps!!