Chemistry IA · Reactivity 2 · How much, how fast, how far? · topic 18 of 25

Does the rate really double every 10 °C? · IB Chemistry IA idea: guide, sample graph and step-by-step plan

no lab, but real thinking: great

Everyone says a reaction runs twice as fast for every 10 °C rise. You're going to test the rule against the theory behind it, and against real activation energies.

Difficulty●●○ Medium
KitComputer only: spreadsheet and published data
TimeAbout 10 hours
FitsHL (Arrhenius); SL: Maxwell–Boltzmann version
  • ✓ you like maths in chemistry
  • ✓ you can build a spreadsheet model
  • ✓ you want to test a rule of thumb

The big idea

← so the rule is true for ONE value

The rule of thumb comes from the exponential factor in the Arrhenius equation, which is proportional to the fraction of collisions with at least the activation energy. That fraction changes with temperature by a factor you can calculate for any Eₐ. So there is one special value of activation energy for which the rule is exactly true, and the rule fails above and below it. Build the model, scan across Eₐ, then check where real reactions fall, using published values. Spreadsheet work, no apparatus, but the thinking must be careful.

Make it yours: pick one twist

Copying a classic won't show your choices. Pick one of these (or invent your own) and your IA becomes yours.

Swipe for more twists →

Test the model against real rate data

Take published rate constants for one reaction at several temperatures and compare their ratios with the model's.

→ Adds a real-data test: your graph now shows measured ratios against model ratios. Needs a source that gives rate constants, not just activation energies.
Change the temperature range

Repeat for a 10 K rise starting from 273 K, 298 K and 350 K.

→ Tests whether the rule depends on where you start. The graph gets a family of curves.
Use the full Maxwell–Boltzmann tail

Calculate the fraction above Eₐ by integrating the distribution rather than using the exponential alone.

→ A more accurate model that you compare with the simple one. Stretch maths, and you must justify your method.
Group the reactions

Sort database reactions by type, such as gas-phase radical reactions and reactions in solution, and compare their typical Eₐ.

→ Your question becomes: which kinds of reaction obey the rule? Needs a sampling rule you can defend.
Switch to a rise of 5 K or 20 K

Test whether a rule 'doubles per 10 K' scales sensibly to other steps.

→ Checks whether the rule is really exponential, and gives you a new graph of ratio against temperature step.
Change the context

Food storage, cold chains, or fever in biological reactions.

→ Gives your introduction a purpose; the model and graph stay the same.

Your Chemistry IA research question: run the check

write it FIRST, then check it

Write your own question first. Then make sure it ticks every box:

  • Names the independent variable (the activation energy, with a range in kJ mol⁻¹) and the starting temperature.
  • Names the dependent variable as a calculated ratio, and says what that ratio means.
  • Says which model you use and what stays fixed in it (the temperature step, the constants).
  • Says where your real Eₐ values come from, and how you chose which reactions to include.
  • Is narrow enough for about 10 hours, and has enough values of Eₐ to show a curve.

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The model

The picture to draw: the tail beyond Eₐ at two temperatures, and the table you will build. Draw your own with your real model for the Method section.

Eₐenergy of molecules (not to scale)Eₐ / kJ mol⁻¹ratio20……150????formula cell: kelvin and joulesfill down for each Eₐhotter: tail beyond Eₐ is tallerthen chart ratio against Eₐ

How your Chemistry IA could be laid out

The usual order for a topic like this, what each part needs to show, and roughly how much of your 3,000 words it takes. The words are all yours.

Research question and context~250
Your question; where the 10 °C rule is used; the idea you will test.
Background chemistry~450
Activation energy; the Maxwell–Boltzmann picture; the Arrhenius expression; why the exponential factor gives a ratio for a temperature step.
Variablestable
Independent variable (Eₐ), dependent variable (ratio) and what you keep fixed in the model; and for the database part, what you filter.
Method~450
How you built the model; every constant and unit; the range and step of Eₐ; where your real Eₐ values came from and the rules for choosing them. Repeatable by someone else.
Safety, ethics, environment~40
Short and specific: screen use only, so say so, and note the data sources' licences or conditions.
Raw datatable
The model's table of Eₐ against ratio, and the table of database reactions with their source and conditions.
Processing~250
One worked calculation of the ratio, with units checked; how you handled uncertainty in published Eₐ values.
Graphs and analysis~350
Ratio against Eₐ with the model line, the reference line for 'doubles', and your real reactions placed on it. Error bars for Eₐ spread.
Conclusion~400
Answer with numbers: for which Eₐ the rule holds, how far real reactions fall from it, and what your model leaves out.
Evaluation~650, the biggest part!
Limits of the model, limits of the data, ranked by their effect on your conclusion, with improvements linked to each.
Referencesnot counted
Every database, table and paper used, with the date you accessed it.

What your Chemistry IA graph could look like

show the claim you're testing

Made-up reactions placed on the model, for an example start of 310 K, to show you the form of a strong graph, not the answer. Yours will use your own temperatures. example only

01530456075901051201351501234567Activation energy Eₐ / kJ mol⁻¹ (± 5 for a published value)Rate ratio, 310 K → 320 K (example start)model: exp(−Eₐ/RT) ratiothe rule of thumb: ratio = 2reactions from a data table (made up)rule fails below and abovethis Eₐ: how far, and why?ILLUSTRATIVE · MADE-UP DATA
  • Axis labels name the quantity and its unit. The ratio is dimensionless, but say which temperatures it refers to.
  • The dashed line is the claim being tested. The place where the model crosses it is the answer to part of your question.
  • Points from a table sit on the model by construction. The interesting part is where they land along the Eₐ axis, and how wide the Eₐ spread is.
  • The horizontal error bars show the spread in published Eₐ values. Say where it comes from.
  • Another graph to consider: ln of the ratio against Eₐ, which is a straight line in this model, so any departure stands out.

Which assumption matters most?

for a model, assumptions are the uncertainty

Rank by the effect on the calculated ratio at Eₐ = 50 kJ mol⁻¹, not by how obvious the assumption looks. A modelling investigation still has uncertainty: it sits in the inputs and in the model.

Eₐ taken as ± 5 kJ mol⁻¹6.5%Starting at 288 K, not 298 K4.6%Exact tail integral vs exp alone1.6%R rounded to 8.310.03%biggest effect: discuss this first!% change in the ratio, Eₐ = 50 kJ mol⁻¹ (made-up)ILLUSTRATIVE · MADE-UP NUMBERS

Your game plan

Tick steps off as you go. We'll remember on this device.

0 of 11 done

  1. Read and predictFind the Arrhenius equation and decide what quantity changes with temperature when Eₐ is fixed. Predict whether the ratio rises or falls as Eₐ rises.
  2. Plan the modelDecide what you keep fixed (the start temperature, the step) and what you vary. Write the units for R and Eₐ before you type a formula.
  3. Trial run (1 lesson)Build a small version for three values of Eₐ. Check one value by hand with a calculator. Is the ratio sensible? Do the units cancel?
  4. Decide your data source and sampling ruleChoose where your real activation energies will come from and how you decide which reactions go in. State the rule before you look at the values.
  5. Build and extend the modelFill down across your range of Eₐ with enough values to see the curve. Save a labelled copy so you can show your work.
  6. Collect the database valuesRecord each reaction, its Eₐ, the conditions and the source. Note when the data are for a limited range of temperature.
  7. Graph and comparePlot the model, the reference line and the real reactions together. Decide how to show the spread of the published values.
  8. InterpretWhere does the rule hold? Where does it fail, and by how much? What does the model leave out, such as the pre-exponential factor and the mechanism?
  9. EvaluateWhich assumption or input changes the ratio most? Rank them and make every improvement specific.
  10. Write, then cutWrite in the order of the layout above. Keep within 3,000 words: tables, graphs, equations and references are not counted, so let them carry detail.
  11. Check before your teacher's draftRun the checklist below, then get your RQ or draft checked. Your teacher reads one draft only, so make it count.

Chemistry you'll need

Traps to avoid in this Chemistry IA

  • Using °C in the exponent: temperatures must be in kelvin.
  • Mixing kJ mol⁻¹ and J mol⁻¹ with an R that is in J mol⁻¹ K⁻¹. The ratio will be wildly wrong.
  • Treating the rule of thumb as a law. The model has one value of Eₐ for which it works, and your conclusion should say where.
  • Picking only the reactions that agree with the rule, with no sampling rule stated.
  • Forgetting that the rate depends on more than the fraction above Eₐ: orientation, concentration and mechanism are all left out.
  • Calling it an experiment with no discussion of the model's limits. For a model, the limits are the evaluation.

More Chemistry IA ideas like this

Make sure it's yours

This guide shows how a topic like this is usually approached. It is not an IA. Your question, choices, data, analysis and words must be your own: change something, tell your teacher where the idea came from, and follow your school's rules on outside help.

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