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I conducted a lab in which different concentrations of $\ce{HCl}$ were used and $\ce{Na2CO3}$ was added. The pressure change was measured for a reaction with the different concentrations.

Now I am going to find the reaction rate for the reactions. I am thinking that using the pressure data, I can find the reaction rate by doing the following.

Consider:


${PV = nRT}$ ($R$ and $T$ are constant so they can be taken out of the equation)

${PV = n}$

$P = {\frac nV}$ (Knowing that $\text{c}={\frac nV}$)

${P} = \text{c}$


Seeing as pressure is directly related to concentration, then couldn't I just use the pressure data to find the rate and then relate that to the concentration change over time?

The alternative would be to use ${PV=nRT}$ for each second of the reaction and find the concentration change that way. However, I want to consider the possibility of doing it this way.

One problem I forecast would be the units: kPa/s vs. mols/L

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    $\begingroup$ You can't "take out" $R$ and $T$ from the ideal gas equation. If you do not know the value for a variable, then the most you can do is try to cancel it out in a ratio: $\frac{P_1V_1}{P_2V_2}=\frac{n_1RT}{n_2RT}=\frac{n_1}{n_2}$ $\endgroup$ – Nicolau Saker Neto Nov 24 '13 at 19:10
  • $\begingroup$ What I'm trying to say is that during the experiment Temperature was constant .. I based my information on this chemguide.co.uk/physical/basicrates/pressure.html $\endgroup$ – Ds.109 Nov 25 '13 at 1:56