Chemistry · Grades 10–12
Physical chemistry · Formula reference 1
Formula reference
Rule and assumptions
pH from a supplied concentration
Use the dilute idealized aqueous model; concentrations approximate activities.
pH ≈ −log₁₀([H₃O⁺]/(1 mol/L))
pOH at 25 °C
The sum pH + pOH is approximately 14 for the stated dilute aqueous model at 25 °C; it changes with temperature.
pOH ≈ 14 − pH at 25 °C
Gas pressure at fixed temperature
For a fixed amount of ideal gas at constant temperature, pressure increases as volume decreases.
P₂ = P₁V₁/V₂
Ideal-gas volume
Use absolute temperature in kelvins. With R = 8.314 kPa·L/(mol·K), pressure in kPa gives volume in litres.
V = nRT/P; R = 8.314 kPa·L/(mol·K)
Bond-enthalpy estimate
Bond breaking requires energy; bond formation releases it. Average bond energies give an approximate reaction enthalpy.
ΔH ≈ bonds broken − bonds formed
Further reading and review references
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Learning preview · independent educational and translation review required. Suggested grades are not official curriculum alignment.