### Video Transcript

According to the equation shown, how many moles of CO₂ would be produced if 7.5 grammes of ethane, molar mass 30 grammes per mole, was burned completely to form carbon dioxide and water? 2C₂H₆ gas plus 7O₂ gas react to form 4CO₂ gas plus 6H₂O gas. A) 0.5 moles, B) 1.0 moles, C) 2.0 moles, D) 3.0 moles, or E) 4.0 moles.

CO₂ is, of course, the symbol for carbon dioxide. And C₂H₆ is the formula for ethane. Ethane is a very simple hydrocarbon. And it’s one of the simplest alkanes. Here, it’s being combusted with oxygen to form carbon dioxide and water. Our job is to find the amount in moles of carbon dioxide produced when we burn 7.5 grammes of ethane.

The first thing we need to do is calculate the amount in moles of ethane in 7.5 grammes. And then, we can use the chemical equation to work out how much CO₂ we’ll get for that amount of ethane. The first thing we do is take the mass of ethane and divide it by its molar mass, so 7.5 grammes multiplied by one mole per 30 grammes. If we evaluate it at this point, we’d get 0.25 moles of ethane.

And then, we have to convert to moles of CO₂. And we do this by observing that the equation tells us that we get four moles of CO₂ out for every two moles of ethane in. So, we can simply multiply the amount of ethane by four moles of CO₂ per two moles of C₂H₆. Of course, you could’ve simplified it to two moles of CO₂ per mole of ethane, but we get the same answer. After cancelling units, we’re in moles of CO₂. And our final answer is 0.5 moles of carbon dioxide. So, when we burn completely in oxygen 7.5 grammes of ethane, we’ll produce 0.5 moles of carbon dioxide.