Entropy, Gibbs energy and feasibility
مُقدَّم| English | المعنى |
|---|---|
| entropy/ˈentrəpi/ | انتروبيا |
| Gibbs energy/ɡɪbz ˈenədʒi/ | طاقة جيبس |
What would explain this observation?
- A reaction can be endothermic and still be thermodynamically favourable. Enthalpy alone does not determine the direction favoured at a given temperature.
Build the model
- Entropy 熵 is associated with energy dispersal and the number of accessible microscopic arrangements.
- Gibbs energy 吉布斯能 combines enthalpy, entropy and absolute temperature for a process at constant temperature and pressure.
- entropy: A state property related to energy dispersal and accessible arrangements.
- Gibbs energy: A thermodynamic quantity combining enthalpy and entropy contributions.
What can remain small even when ΔG is negative?
الصعوبة 1/5 · 100 عملة + مكافأة صغيرة عند الإكمال الأول اليوم
Delta G says whether a reaction is thermodynamically favourable; it says nothing about kinetics. A high activation barrier can keep a favourable reaction immeasurably slow, as diamond shows.
Match each technical term to its precise meaning.
الصعوبة 2/5 · 140 عملة + مكافأة صغيرة عند الإكمال الأول اليوم
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Use ΔG = ΔH - TΔS with consistent energy units.
- A negative Gibbs energy change indicates thermodynamic favourability for the stated conditions, not a fast rate.
- An activation barrier can make a favourable process slow.
In the lab: State whether values are standard-state quantities and record temperature in kelvin. Convert entropy from joules per kelvin per mole into kilojoules per kelvin per mole when enthalpy is in kilojoules per mole.
Which two habits make the investigation or model in this case more defensible?
الصعوبة 2/5 · 140 عملة + مكافأة صغيرة عند الإكمال الأول اليوم
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: ΔH = +20 kJ per mole, ΔS = +100 J per kelvin per mole and T = 300 K.
- Convert ΔS = 0.100 kJ per kelvin per mole. ΔG = ΔH - TΔS = 20 - 300×0.100 = -10 kJ per mole.
- The process is favourable under the stated approximation.
Your turn: ΔH=30 kJ per mole, ΔS=0.10 kJ per kelvin per mole and T=400 K. Find ΔG.
ΔH=30 kJ per mole, ΔS=0.10 kJ per kelvin per mole and T=400 K. Find ΔG.
الصعوبة 2/5 · 140 عملة + مكافأة صغيرة عند الإكمال الأول اليوم
The result is -10 kJ/mol. Known: delta H = 30 kJ per mole; delta S = 0.10 kJ per kelvin per mole; T = 400 K. Use delta G = delta H - T x delta S. Delta G = 30 - 400 x 0.10 = -10 kJ per mole. Negative, so feasible under this approximation; note delta S was already in kJ.
Check the conclusion and its limits
- Thermodynamic favourability does not establish reaction rate.
- Celsius cannot replace kelvin in TΔS, and a unit conversion error can change the result by a factor of 1,000.
Not true: A thermodynamically favourable reaction must be fast. Feasibility and speed are different questions. Thermodynamics (delta G) says a reaction can proceed; kinetics (activation energy, rate) says how fast. Diamond to graphite is favourable yet imperceptibly slow.
- Entropy is associated with energy dispersal and the number of accessible microscopic arrangements.
- Use ΔG = ΔH - TΔS with consistent energy units.
- Watch for: thermodynamic favourability does not establish reaction rate.
Write from a Gibbs energy change of plus 8 kJ per mole
- Delta H is plus 40 kJ per mole. Delta S is plus 80 J per kelvin per mole. The temperature is 400 K.
- Find delta G. A favourable reaction is not necessarily fast.
Feasibility and speed are different questions.
الصعوبة 1/5 · 100 عملة + مكافأة صغيرة عند الإكمال الأول اليوم
True. Feasibility and speed are different questions. Thermodynamics (delta G) says a reaction can proceed; kinetics (activation energy, rate) says how fast. Diamond to graphite is favourable yet imperceptibly slow.
A state property related to energy dispersal and accessible arrangements: write the technical term.
الصعوبة 1/5 · 100 عملة + مكافأة صغيرة عند الإكمال الأول اليوم
entropy means A state property related to energy dispersal and accessible arrangements.
Delta H is plus 40 kJ per mole, delta S is plus 80 J per kelvin per mole, and the temperature is 400 K. What is delta G, and why does a negative value not prove the reaction is fast?
Delta G is delta H minus temperature times delta S, with delta S in kJ. The sign answers feasibility, not speed.
What is delta G?
الصعوبة 1/5 · 100 عملة + مكافأة صغيرة عند الإكمال الأول اليوم
40 minus 32 is plus 8 kJ per mole. The worked example uses different values and gives minus 10.