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how's it going guys in this video we're going to continue on in the series of reaction rates and this time we're going to calculate the initial rate based on a m and k if we already have those so here we have the the standard formula that's going to be k the rate constant times a which is going to be the concentration of one of the reactants or all of the reactants depending and then m to alter the power of m and m is just the order of the reaction they're going to follow these general formulas here so without further ado we're going to jump back into the same problems that we have been going over only this time we're calculating the initial rate so in this first one here um what we're going to go for is what would be the ir we'll say the initial rate if the concentration of a equals 0.95 m and in this case what we solved in the pre in two videos ago now the rate for this is equal to um k times a and it's going to be a second order and then from there what we solved is we have our k value our k value from the previous video is 8.44 m minus 1s so we're just going to plug that in i'm sorry that should be our rate and then we have a which is going to be our 0.95 which they gave us and that's squared okay so we're going to get our rate is equal to 8.44 m to the negative 1 s and that is going to be times 0.9025 now just multiply that out our rate is going to equal 7.6171 which we can say is seven point six one uh we'll make it six two we'll round it off and then let's calculate our units really quick so it gave us in standard m and that's just m2 because it's squared it's second order so we have m2 compared to what we have it in the table as which is m1s equals m2 we divided both sides by m2 m2 what we're going to be left with it's essentially this negative 1 plus 2 is equal to 1. so we're just left with ms perfect so that's going to be our first one and then let's just move down and do the next one all right so here we go we discovered in the last one that the rate was okay times a a was second order and then b in this case was just first order so that's our rate that we're working with here and we're going to say what would be the ir or the rate if the concentration of a is equal to 0.66 molar and the concentration of b is going to be 0.84 molar so now we've got some new concentrations we can plug in and see how they work out in this equation so our rate is going to equal k times a 2 b rate is equal to what we had for our k value was 1 9 7 5 m to the negative 2 s and then that's going to be multiplied by our a squared which is going to be 0.66 squared and then that's going to be 0.84 these are both m rate's going to be 1975. times 0.4356 and then we have our 0.84 okay so i got 722.66 and let's see what those units are going to be so we had units as m to the negative 2 s times m 2 times m so we're going to be left with is negative 2 plus 2 plus 1 equals 1 and we're going to end with 722.66 ms and in these problems one thing it's i think it's always good to double check your units because theoretically you want to make sure that whatever the rate is that you end up with math in terms of the units matches what is given in the table because essentially all these calculations that you've been making were based on those units so in like for instance your k value was based on those units so it's always good to check that all right cool so now we'll move to the last one okay so this is the longer reaction it's got a whole bunch of zeros there as you can see in this case it's going to say we'll say what will the initial rate be if bro3 minus equals 0.940 0.0940 and we'll make br 0.0520 and then h plus will be 0.1850 so it's giving us these these calculations here and as you can see the hydrogen is much higher the concentration here is much higher uh than than even the you know the 940 but what we have here is our rate which we calculated in the previous problem in the previous video sorry bro3 minus second order then we had our br which was third order and our hydrogen ions zero order so they essentially no matter how high this concentration gets it's not going to have any impact on the rate of the reaction it's it's it's basically relevant in in terms of these so our rate is going to equal to k and let me see what else we got we got 0.0940 squared 0.0520 cubed sub in my k value what we got for k was 1.49 times 10 to the seventh m negative four s negative one so there's our k value and then i'll multiply these out eight point eight three six i'm gonna just write it underneath just to save room 10 to the third negative third and then we have 1.41 times 10 to the negative fourth all right so what i got here is that the rate is 18.51 and then we're going to calculate our units so unit check right over here so we had is we had our k value which was m negative 4 s negative 1. and that was multiplied by what would be m squared and then m cubed because we had a second order and a third order and then so what we're gonna have is negative four plus 2 plus 3 equals 1. and what that is gonna do is it's going to we're going to check it against the table that we're given and that all these calculations were based on and it checks out so we have m s negative 1 just like it is in the table and there we go that's how to calculate initial rate so yeah hopefully this helps someone out and