1.7.3Physical Chemistry
Maxwell–Boltzmann Distributions — AQA AS Chemistry Revision Notes & Topical Questions
5 min read 4 parts Lesson 42 of 102
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Features of the Curve
Axes
- Axes The x-axis shows the energy of molecules and the y-axis shows the number of molecules with each energy.
Origin
- Origin The curve starts at the origin because no molecules have zero energy.
Peak
- Peak The peak represents the most probable energy, and the curve is asymmetric, with a long tail to higher energies.
Asymptote
- Asymptote The curve never touches the x-axis at high energy, since there is no upper limit to the energy a molecule could have.
Area
- Area The area under the curve equals the total number of molecules, so it stays constant for a fixed amount of gas.
Part 2 of 4Activation Energy on the Curve
Activation Energy on the Curve
Ea line
- Ea line A vertical line drawn at the activation energy divides the curve into two regions.
Right of Ea
- Right of Ea The area to the right of Ea represents molecules with enough energy to react on collision.
Left of Ea
- Left of Ea The area to the left represents molecules with less than the activation energy, which cannot react.
Small fraction
- Small fraction For most reactions at room temperature only a small fraction of molecules have energy of at least Ea.
Part 3 of 4Reading and Sketching
1
Draw axes labelled energy and number of molecules, and start the curve at the origin.
2
Draw a smooth, asymmetric curve with a single peak that tails off towards the axis without touching it.
3
Mark the activation energy as a vertical line to the right of the peak.
4
Shade the area to the right of Ea to show the molecules able to react.
5
When the temperature changes, draw a second curve with the same area but a different shape and position.
Part 4 of 4Exam Checklist & Tips
1.7.3 – Key Points for the Exam
- Maxwell–Boltzmann distribution A graph showing how the energies of molecules in a gas are spread.
- Most probable energy The energy at the peak of the curve, possessed by the greatest number of molecules.
- Activation energy The minimum energy needed for colliding molecules to react.
- Asymptote A line that a curve approaches but never reaches.
Common Mistakes
- Drawing the curve so that it touches or crosses the x-axis at high energy.
- Starting the curve on the y-axis rather than at the origin.
- Stating that molecules at the peak have the activation energy.
- Changing the area under the curve when the temperature is changed.
Last updated:
\n