Standard Temperature and Pressure

standard temperature and pressure. Abbreviated as STP is a commonly used term in calculations involving gas, is now we're going to say at STP the temperature is measured as either zero degrees Celsius or 273. Kelvin. Now we know that when we're dealing with gas calculations, we tend to go with Kelvin. Now the pressure at STP is one atmosphere. So just remember, when you hear STP, it means 273.15 Kelvin and for pressure, one atmosphere.

here in this example question. It says a sample of oxygen gas has a measured volume of 325 m. Els at STP. How many grams are present? All right, so here they're giving us volume in the forms of milliliters. An STP is giving us temperature plus pressure. We know from the ideal gas law with these values given to us or these variables given to us. The only thing that's missing is our moles. Because we have volume already. We have pressure and temperature and we always know what our is. So we're gonna divide op rt And when we do that, we're gonna get our moles. Moles here will equal pressure times volume over our Times team at STP. Our pressure is one atmosphere, our volume We just change middle leaders toe leaders. So 0.3 to 5 leaders, we have our our constant, which is 0.8 to 06 leaders times atmospheres over moles times K. Then remember, we're dealing with temperature at STP. We used the units off Kelvin, so that's to 73.15 Kelvin. So here Kelvin's council out leaders cancel out atmospheres cancel out and we'll be left with the moles off our oxygen gas. When we plugged that in, we get 0.1450 moles of But here the question is not asking us to determine the moles of oxygen gas, but instead the grams off oxygen gas. So we just need to do a simple conversion. We say that for every one mole of 02 it weighs g because there's two oxygen's those cancel out, but we get at the end is 0.464 g of CO. Two. Here are answer has three significant figures because the value of 3 has three significant figures as well. So just remember when we're faced a question like this, look and see what variables are given. Since we're dealing with the ideal gas law, we see that the value that's missing is moles. Then go for moles to grams to get your final answer

with the idea of STP were faced with a new idea the standard molar volume. Now we're going to say that it represents the volume of one mole of an ideal gas at STP. Alright, so here we're gonna say volume equals moles. Times are t overpay. We're dealing with one mole of the gas Are is just are constant And we're gonna say we're dealing with STP. So our pressure will be to 73.15 Kelvin and our pressure will just simply be one atmosphere we see here that the moles cancel out Kelvin's cancel out atmospheres cancel out. So here we'll have our volume and leaders. When we plug this in, we get 22.4 leaders. This would represent our standard molar volume for one mole of gas and ideal gas. Now this helps to establish a relationship between moles and volumes. And because we have a relationship between Moland volumes, we can create a new conversion factor. And that conversion factor would be that for any one mole of an ideal gas at STP, it's Moeller volume would be 22 4 leaders. So just remember, if we're dealing with STP and we're dealing with one mole of any gas, then it's standard molar. Volume will be 22.4 leaders

here. The example. Question says how many moles of chlorine gas occupy a volume of 15.7 leaders at STP? Alright, so here they're talking about determining the moles of an ideal gas. They're giving us the volume off that gas at STP here. We can use the conversion factor that we know exists with standard molar volume. We're going to say we have 15.7 leaders and we're gonna say here that the conversion factor is for every one mole of any gas at STP, the volume is 24 22 4 leaders here leaders cancel out and I'll have my moles, which comes out 2.701 moles off C l two. So this is one way that we get our answer. What else we could do is we could have also said that we have 15.7 leaders, which is our volume. And then we have STP, which is pressure and temperature. We could have said that are moles equals P V over r T and we would have gotten the same exact answer because here this would have been one atmosphere this year is 15 7 leaders. Then here we have our our constant with its units. Don't forget the units. Times temperature at STP is to 73.15 kelvin, and if we worked it out, we get the same exact moles for l two. So just realize that there's two ways that we can approach a question like this, using it with the conversion factor of one mole for every 22.4 leaders, or by using it through traditional means with the ideal gas law.