[Music] hi everyone my name is andre and welcome back to another educational video from med school eu and today we are going to talk about the ideal gas law now ideal gases are also part of the composition of matter unit so i do want to address it and today i'm going to go over a little bit about the um what our ideal gas is what are the what is the formula what is the ideal guess formula and the equation that we're going to use um and some of the most common calculations that are involved with the imats an ideal gas has zero particle volume and there are no intermolecular forces of attraction now what does it mean i mean like gases are still going to have intermolecular forces they are still going to have particle volume but why it's counted as an ideal gas is that the particle volume is so tiny and the intermolecular forces are so tiny that we consider them negligent and so therefore they're not going to be counted as part of the equations because if they are counted as part of the equations well then that's going to change everything and our ideal gas formula or ideal gas equation is simply not going to be accurate but the only reason it does turn out to be accurate is because we assume that the gases that are involved within our equation or the ones that we're calculating they have zero particle volume and no intermolecular forces between them now we can confidently say that volume is dependent on two primary factors and that is going to be temperature measured in kelvin and pressure that's typically measured in pascals or kilopascals now the pressure of gas so if you're talking about gas that is in a confined container right and you have plenty of gases in the container the pressure of gas where does it where does it come from i mean if you have a balloon right and you're squeezing down on the balloon it's exerting a pressure against you against your hands as you're pushing it down and eventually the balloon is going to pop if you keep doing that and the reason for that is because is is because it's decreasing the volume and when you're decreasing the volume you're increasing the pressure so they're going to have an inverse relationship between if you are decreasing pressure you will increase volume and vice versa and so uh in terms of containers where this pressure come from in terms of gases they're not solids right they're not liquids where does the pressure come from well the pressure of gases comes from the the gas molecules colliding to the with within their walls and other gas molecules within the container that's what produces the pressure now the ideal gas formula is pv equals nrt so here what we've got is p is of course pressure in atm atmospheres or kilopascals depending on which units you're going to be using or which units are given volume is going to be measured in liters we're going to have n that is number of moles r is going to be a constant and so the the constant measure that we're going to typically use is probably going to be 0.0821 liters atm over kelvin times moles so this is this is the typical constant that we're going to use and a temperature will always always always be measured in kelvin now if you want to know a conversion between um degrees celsius to kelvin you would have to add 273 to get kelvin so sometimes on the imat you will be given degrees in in celsius and you're going to have to convert them to calvin by just knowing this simple conversion now i'm not sure how useful this is going to be for you but something to consider is that one atmospheric pressure is going to be equal to 101.3 kilopascals that is another unit of conversion now another point of discussion here is that one mole of an ideal gas will take up 22.4 liters of volume at stp what does stp mean it stands for standard temperature and pressure and what that means is is a standard temperature is zero degrees celsius or 273 kelvin and standard pressure is going to be 1 atm or a 101.3 kilopascals so when you are given a question that states that a gas is at stp you can make the assumption that the gas is an ideal gas and therefore you can use this uh sort of conversion so if it's asking you for the volume that the gas takes up then you can use the conversion from most of all to two liters or if it's asking you for the moles then you can make the conversion from volume to the moles using this same conversion and this is something that's not given on the test so i suggest you memorize it and and you use it and practice with it before writing the imat so now here we're going to get a chance to use our pvnrt formula if a person exhaled 125 milliliters of carbon dioxide gas at 37 degrees celsius and 0.95 atm of pressure what would this volume be at a colder temperature of 10 degrees celsius and 0.9 atm of pressure so what i gather from here is we have two situations the first situation gives us everything except for moles except for n and the second situation gives us just the pressure and the temperature so what we're going to have to do is basically find our number of moles so that then we can find the volume the second volume that is uh being measured so we're going to have to do pvnrt twice so uh first of all i'm going to convert the 37 degrees celsius into kelvin that will be 310 kelvin that is the temperature that we begin with so the formula is pv equals nrt now in order to isolate for the moles n is going to be pv over rt and i'm not going to go over the math here right now and and how i got there that's going to be something that will be dealt with with the math unit so if you cannot do this basic conversion i suggest you drop chemistry right now and you go do a little bit of basic algebra so now we are going to substitute all of our variables in for the first situation so our pressure is 0.95 0 atm that will be multiplied by the volume i'm going to convert the volume into liters so that'll be 0.125 liters also you're going to need to learn some basic unit conversions like milliliters to liters and degrees celsius to kelvin possibly atmospheres to kilopascals you're going to have to learn some basic unit conversions along the way that will be over r so our constant is going to be 0.0821 liters times atm over kelvin times mole and that will be multiplied by 310 kelvin in terms of temperature so now i can cancel our units kelvin will cancel with kelvin liters with liters atmospheres with atmospheres and now because this is in the denominator of the denominator we are going to get our units as moles so let's do the calculation here so our answer is going to be 4.67 times 10 to the negative 3 moles and i would suggest you also learn how to convert from decimals to scientific notation for the chemistry unit as well now i'm going to rearrange my formula to find the new volume with the new temperature so volume will equal nrt over p this will now equal to 4.67 times 10 to the negative 3 moles that we calculated within our previous equation r is going to see the same 0.0821 remember it's a constant so it remains the same our temperature is now going to be 10 degrees celsius so 10 degrees plus 273 is going to be 283 kelvin all over new pressure of 0.900 atm now let's do the cancellations atmospheres cancel with atmospheres our moles will cancel with moles kelvin will with kelvin and we're left with liters on the numerator of the numerator the answer is 0.12 liters next is going to be a little bit of stoichiometry and we're going to get into stoichiometry a little bit later in chemistry but for now since this involves the ideal gases and the ideal gas equation i figured i might as well bring it up so the question is what is the stp volume of 10 grams of methane gas again i've mentioned this previously stp stands for standard temperature and pressure which indicates to me that it is talking about an ideal gas therefore i can use the conversion of one mole to the 22.4 liters of volume it's asking for the volume so again what we're going to have to do is take 10 grams of methane gas and turn it into moles and then turn it into our liters for the volume so first always start with what's given i'm given grams and i need to get to liters of volume i cannot go there directly so what i'm going to have to do is convert it to moles because i'm going to know what the molar mass of methane is by looking at the periodic table and from moles i'm going to be able to go into liters using that 22.4 conversion that we have at stp so let's begin we've got 10.0 grams of methane gas now the formula for methane gas and this is something we're going to learn in organic chemistry that is ch4 so now what we're going to have to do is use the periodic table to add up the molar mass of carbon and the molar masses of four hydrogens together so carbon's molar mass is 12.01 we're going to add 1.008 the molar mass of hydrogen multiplied by 4 and our our molar mass is going to be 16.043 grams per mole so when i multiply i'm going to have the grams in the denominator in order to cancel with the grams that were given and i'm going to convert that into moles one mole of ch4 this is molar mass this is the reason i can convert that now the grams will cancel with the grams we're left with moles great but i need volume so i'm going to convert moles to volume by doing the conversion of one mole of an ideal gas that is ch4 gas into 22.4 liters so one mole of ch4 ideal gas at stp takes up 22.4 liters of volume now our moles are going to cancel and we're left with with just the liters so let's do the calculation here and we're left with 13.96 liters of c h for gas so this concludes our first video and the first full topic covered in the chemistry section of the imath specifications and in the next lecture we are going to take a look at the atomic structure and we're going to talk about atomic theory [Music] you