Chemistry Help

[Double93]

How many molecules of ammonia, hydrogen and nitrogen are in this equation?

3H (subscript 2) + N (subscript 2) ---> 2NH (subscript 3)

[Double93]

I quite agree! I do prefer to get pointed in the right direction so that i can learn and remember for the future!

[Double93]

Could I ask for a little assistance with another question please?

If walking uses 12.6 kJ kg-1 h-1 (12.6 kJ of energy per kg of your body weight per hour) how much time (in hours) would you have to walk to expend the energy provided by the fat you consumed during the 24 hours in which you kept your food diary (the energy value for fat in your pie chart)? Give your answer as a decimal number to three significant figures.

Lets say :

The persons body weight is 52kg
and
The fat consumed in 24 hours was 33g.

How on earth do i figure this out? :S

[bhg481]

It sounds like you have a chart somewhere which gives the energy value for fat in kJ/g, call it C.
You have consumed 33g of fat in the 24 hours, which enables you to work out how many kJ you have consumed using the value C above.
You know the body weight of the person and you know that for each Kg of body weight you consume 12.6k every hour.
You burn 12.6kJ of energy for each kg of body weight per hour. That gives you all the information you need to find out how many kg per hour a 52kg person weighs and so, how long it will take to burm off the energy consumed.

[Double93]

Basically, i had to keep a 24hr food diary and calculate the total amount of proteins, carbs and fats consumed in that time period. These 3 totals were put into a spreadsheet and after a calculation on the spreadsheet- you ended up with 3 other numbers (i assume is the grams changed to kJ, so 33g of fat is 1221kJ?)
This was then changed into a pie chart (all of which i have done) and then the above question followed!

[bhg481]

IF your figure of 1221kJ is correct for 33g fat (I have no way of knowing this) then that is the energy you have burned in 24 hours.
As a 52kg person, you burn 52 x 12.6 kJ/hour walking - this is the burn rate.
if you divide the energy burned by the burn rate in hours then you get the number of hours it will take to burn that energy.

[Double93]

Once i had the 3 totals of fat, carbs and protein for the 24 hour period- i used the spreadsheet to calculate the amount of energy provided by each macronutrient. There is a table provided with an energy density/kJ g-1 and for fat the number 37 is present. I was instructed to put =B1*37 in the spreadsheet and 1221 was the result. So assuming that i have done my previous stages correctly, i do believe 1221 is correct!
Therefore by burn rate is 655.2, so 1221/655.2=1.86h

[bhg481]

That sounds right.

Incidentally, you would have been better starting a new thread for this question. I only saw it by accident; a new thread would have put your question at the top of the science category and made it more visible.

[bhg481]

Final tip - read the question VERY carefully, then look again at your answer.

[Double93]

Hmmm... is it to do with the 1.86? Do i need to convert it? 1 hour 51.6 minutes to 3 sig figs = 1.52 hrs?

[bhg481]

Sorry, I misread the question. I read it as 3 decimal places (not 3 significant figures), your answer was correct.

[Double93]

Thank you very much :D