You first have to find out how many half lifes there is overall. So you can keep halving from 100 until you get to 12.5. 100 - 50 - 25 - 12.5 which equates to 3 half lifes because it has been halved 3 times. So now you know there are 3 half lifes in 24 minutes so to find the length of one you do 24/3 which = 8 minutes and therefore one half life is 8 minutes. Hope that helped!
You first have to find out how many half lifes there is overall. So you can keep halving from 100 until you get to 4. 100 - 50 - 25 - 12.5 which equates to 3 half lifes because it has been halved 3 times. So now you know there are 3 half lifes in 24 minutes so to find the length of one you do 24/3 which = 8 minutes and therefore one half life is 8 minutes. Hope that helped!
If the initial concentration in a first order reaction [would it be any different if it was a zero or a second order reaction??] with a half life of 12 minutes was 0.400 moldm-3, what would the concentration be after 48 minutes?
If the initial concentration in a first order reaction [would it be any different if it was a zero or a second order reaction??] with a half life of 12 minutes was 0.400 moldm-3, what would the concentration be after 48 minutes?
With a half life of 12 minutes, in 48 minutes there would be 4 half lifes that have occurred as 48/12 = 4. So then you must half the concentration a total of 4 times. 0.400 - 0.200 - 0.100 - 0.05 - 0.025. So your final answer is 0.025moldm^-3. Also first order reactions are when the rate of reaction is directly proportional to the change in one reactant and therefore half life can be calculated accurately. In a second order reaction the rate depends on two substances and therefore half life cannot be calculated as accurately and it becomes a more complex calculation.
With a half life of 12 minutes, in 48 minutes there would be 4 half lifes that have occurred as 48/12 = 4. So then you must half the concentration a total of 4 times. 0.400 - 0.200 - 0.100 - 0.05 - 0.025. So your final answer is 0.025moldm^-3. Also first order reactions are when the rate of reaction is directly proportional to the change in one reactant and therefore half life can be calculated accurately. In a second order reaction the rate depends on two substances and therefore half life cannot be calculated as accurately and it becomes a more complex calculation.
I see thank you so much! So do you think we'll only be asked half-life questions for 'a first order' at A2? I'm doing Edexcel.