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# Converting from cm3s-1 to moldm-3s-1 without drawing a graph watch

1. Hey all!

I'm doing the A2 Chemistry B Salters coursework, magnesium and acids, and I'm currently doing the analysis for my data

I've found my rate equation and total order, but I'm stuck on how to find a value for "k" when my rate does not have the right units, does anyone know how to convert from cm3s-1 to moldm-3s-1 without the need to draw a graph?

Any help is appreciated! Thanks
2. (Original post by Francesca Lucia)
Hey all!

I'm doing the A2 Chemistry B Salters coursework, magnesium and acids, and I'm currently doing the analysis for my data

I've found my rate equation and total order, but I'm stuck on how to find a value for "k" when my rate does not have the right units, does anyone know how to convert from cm3s-1 to moldm-3s-1 without the need to draw a graph?

Any help is appreciated! Thanks
Presumably cm3 of gas.

Volume of gas ===> moles of gas (volume/24 @room temp)

Moles of gas ====> moles of reagent reacted (use the equation stoichiometry)

Moles of reagent reacted ===> new solution concentration (molarity = moles/vol)
3. (Original post by charco)
Presumably cm3 of gas.

Volume of gas ===> moles of gas (volume/24 @room temp)

Moles of gas ====> moles of reagent reacted (use the equation stoichiometry)

Moles of reagent reacted ===> new solution concentration (molarity = moles/vol)
Thanks! Why do the moles of reagent reacted need to be calculated if at the end you just do moles/vol?
4. (Original post by Francesca Lucia)
Thanks! Why do the moles of reagent reacted need to be calculated if at the end you just do moles/vol?
Because rate of reaction is always calculated as the change in moles per litre of reagent per unit time ...
5. (Original post by charco)
Because rate of reaction is always calculated as the change in moles per litre of reagent per unit time ...
I'm confused as to how the two fit together though?
6. (Original post by Francesca Lucia)
I'm confused as to how the two fit together though?
The reaction of the acid (say) produces a gas.

You want to know how the concentration of the acid decreases with time.

You find the moles of gas ===> get the moles of acid reacted ===> calculate change in acid concentration.
7. (Original post by charco)
The reaction of the acid (say) produces a gas.

You want to know how the concentration of the acid decreases with time.

You find the moles of gas ===> get the moles of acid reacted ===> calculate change in acid concentration.
Oh right, it was the way you had worded it before. Makes much more sense now, thank you
8. (Original post by charco)
The reaction of the acid (say) produces a gas.

You want to know how the concentration of the acid decreases with time.

You find the moles of gas ===> get the moles of acid reacted ===> calculate change in acid concentration.
Sorry, quick silly question, your help has been brilliant and I'm finally getting there - but when calculating the change in acid concentration, is it the moles of the acid/volume of the acid or /volume of the has produced?
9. (Original post by Francesca Lucia)
Sorry, quick silly question, your help has been brilliant and I'm finally getting there - but when calculating the change in acid concentration, is it the moles of the acid/volume of the acid or /volume of the has produced?
Concentration is always moles of solute / volume of solution
10. (Original post by charco)
Concentration is always moles of solute / volume of solution
Thank you, you've been a great help!

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