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My experiment involves the reaction between sodium bicarbonate and acetic acid. I'll be changing the temperature between each trial and measuring the change in pressure by the gas produced. From here I hope to determine the rate expression, rate constant, activation energy then finally produce an Arrhenius plot.

My question is since this reaction is endothermic, how do I account for the change in temperature as the reaction proceeds? I also can't seem to find any published literature value for this reaction's activation energy or enthalpy change, and would love it if someone pointed out a database or something similar.

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For this experiment to work, you need good control of your temperature profile. In other words the temperature must be somewhat uniform.

If this is the case measure two temperatures.

  • $T_e$ is the isothermal temperature of the experiment.
  • $T_r$ is the temperature at the point of reaction.

If $T_e$ is 10°C, 20°C, 30°C and $T_r$ is 9°C, 18°C, and 29°C then the temperature change can be assumed to have a negligible effect. (You would want to use $T_r$ in the kinetics calculations.)

If $T_e$ is 10°C, 20°C, 30°C and $T_r$ is 4°C, 6°C, and 8°C then the effect is not negligible. Accounting for the endothermic temperature change in the calculations is a poor option because it would add needless complication. A better approach is to keep things simple by revisiting the controls in the experimental design to see what can be done to minimize the endothermic effect. One possibly would be using less reactants.

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  • $\begingroup$ And does there happen to be some sort of standard for determining a negligible effect? $\endgroup$ – CorexTech Aug 30 '16 at 0:45
  • $\begingroup$ This is an experimental statistics question, not really a chemistry question. I suggest posting to cross-validated stats.stackexchange.com so an answer comes from the right type of expert. $\endgroup$ – Agriculturist Aug 31 '16 at 17:33
  • $\begingroup$ If it were me, I would replicate each test 3 times. Take the standard deviation at each temperature. If 5x the standard deviation is less than the differences between $T_e$ then the rule of thumb is the effect is significant. ... In practice it is customary to consult with a statistician on experimental design. A chemist can tell you if the theory is sound. $\endgroup$ – Agriculturist Aug 31 '16 at 17:38

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