| Extension Topic | Does M-B Curve Change? | What Changes the Rate? | | :--- | :--- | :--- | | Increase Temperature | Yes (Flattens, shifts right) | Higher fraction > (E_a) | | Add Catalyst | No | (E_a) decreases (threshold moves left) | | Reduce Pressure/Vacuum | No | Total collisions decrease, but distribution shape same | | Heavier Isotope | Yes (Peak shifts left) | Lower average speed reduces collision frequency |
Use this guide to facilitate discussion, not just to provide answers. The power of POGIL is in the argument—let the students defend why the tail matters more than the peak. | Extension Topic | Does M-B Curve Change
Mastery of these extension questions means a student truly understands the exponential relationship between temperature, activation energy, and rate—a concept that defines modern chemical kinetics. The power of POGIL is in the argument—let
At the same (T), ( \frac12 m v^2 ) is constant on average. Heavier molecules ((^238\textUF_6)) have a lower most probable speed. The two curves overlap significantly but are shifted. shifts right) | Higher fraction >
"The fraction of molecules with sufficient energy is exquisitely sensitive to temperature because (E_a / RT) appears in the exponent. A 100K increase reduces the exponent magnitude, yielding a 150-fold increase in reactive collisions." Part 5: Common Extension Question 4 – Isotopes and Effusion Question: Consider two isotopes: (^235\textUF_6) and (^238\textUF_6) at the same temperature. Draw their M-B distributions. Why is the difference in average speeds small, but the difference in effusion rates significant? Answer Key Reasoning This connects the M-B distribution to Graham's Law of Effusion.
No, the shape does not change.
Effusion rate depends on the average speed ((v_avg = \sqrt\frac8RT\pi M)). The small difference in mass leads to a small difference in average speed.