Zadanie 4e
Ethene reacts with water in the presence of an acid catalyst at room temperature. C2H4(g) + H2O(l) → C2H5OH(l) ΔH⊖ = −44 kJ mol−1 (i) Calculate the change in entropy, ΔS⊖, for this reaction in…
Spontaneity and the sign of ΔG
Interpret a negative ΔG as the criterion for spontaneity at constant pressure, explain how the signs of ΔH and ΔS decide whether a reaction is spontaneous at all, low or high temperatures, and calculate the temperature at which ΔG changes sign.
Tę umiejętność sprawdza 19 zadań wzorowanych na arkuszach IB z lat 2022–2026.
Zadania sprawdzające tę umiejętność: 19 Otwórz w wyszukiwarce z filtrami
Zadanie 22
Under which temperature conditions is ΔG⊖ negative for this reaction? CaCO3(s) → CaO(s) + CO2(g) ΔH⊖ = +178 kJ mol−1 A. Low temperatures only B. High temperatures only C. Any temperatures D. No temperatures
Zadanie 5a
(i) Calculate, in kJ mol−1, the standard enthalpy change of this hydrogenation reaction using the enthalpy of combustion data in section 14 of the data booklet. (ii) The standard entropy change for this reaction is…
Zadanie 24
A reaction is spontaneous at low temperatures but becomes non-spontaneous when the temperature is raised. Which combination of signs of ΔH and ΔS is consistent with this behaviour? A. ΔH > 0 and ΔS > 0 B. ΔH < 0 and…
Zadanie 4b
(i) Using section 12 of the data booklet, determine the standard enthalpy change of the reaction, in kJ mol−1. (ii) A value obtained from bond enthalpies is less accurate than one obtained from enthalpies of formation. State two reasons why.…
Zadanie 3b
When the cell discharges, a spontaneous redox reaction generates a potential difference between the electrodes and the temperature of the cell rises. (i) Deduce the signs of ΔHdischarge, Ecell and ΔGdischarge.…
Zadanie 5d
Pentadecane can be cracked into smaller molecules. Consider the reaction: C15H32(g) → 3 C4H8(g) + C3H8(g) where C4H8 is but-1-ene. (i) Use the bond enthalpies in section 12 of the data booklet to determine ΔH⊖ for this reaction.…
Zadanie 3h
Determine the minimum temperature, in K, at which the forward reaction is spontaneous. Use section 1 of the data booklet. If you were unable to obtain an answer for 3f, use 230 J K−1, but this is not the correct value.
Zadanie 15
The decomposition of calcium carbonate is not spontaneous at low temperatures but is spontaneous at high temperatures. CaCO3(s) → CaO(s) + CO2(g) What are the signs of ΔH⊖ and ΔS⊖ for this reaction?…
Zadanie 17
Which combination of the signs of ΔH⊖ and ΔS⊖ describes a reaction that is spontaneous only at low temperature? The options list the sign of ΔH⊖ first. A. positive, positive B. positive, negative C. negative,…
Zadanie 17
A reversible reaction in a closed vessel at constant temperature and pressure has reached equilibrium. Which statement is correct? A. The change in Gibbs energy, ΔG, is zero B. The standard change in Gibbs energy, ΔG⊖, is zero C.…
Zadanie 5f
(i) Calculate the standard cell potential for the reaction 2 Al(s) + 6 H2O(l) → 2 Al3+(aq) + 6 OH−(aq) + 3 H2(g) Use section 19 of the data booklet. (ii) Deduce whether this reaction is spontaneous under standard conditions at 298 K, and give a reason.
Zadanie 18
Which combination of signs of ΔH and ΔS belongs to a reaction that is not spontaneous at low temperatures but becomes spontaneous at high temperatures? A. ΔH positive and ΔS positive B. ΔH negative and ΔS…
Zadanie 18
A reaction is not spontaneous at low temperatures but becomes spontaneous when the temperature is raised sufficiently. What are the signs of ΔH and ΔS for the reaction? A. ΔH positive, ΔS positive B. ΔH negative, ΔS negative C. ΔH positive, ΔS…
Zadanie 3c
The standard free energy change, ΔG⊖, for the production of methanol is −44.0 kJ at 298 K and the standard enthalpy change, ΔH⊖, is −114 kJ. (i) State, with a reason, whether the production of methanol is spontaneous at 298 K.…
- Materiał graficzny
Zadanie 15
Which row gives the signs of ΔH and ΔS for a reaction that is spontaneous at low temperatures but non-spontaneous at high temperatures? A. ΔH < 0, ΔS < 0 B. ΔH < 0, ΔS > 0 C. ΔH > 0, ΔS < 0 D.…
Zadanie 17
Dividing both sides of the equation ΔG⊖ = ΔH⊖ − TΔS⊖ by −T gives −ΔG⊖/T = −ΔH⊖/T + ΔS⊖. Which term represents the entropy change of the surroundings? A. −ΔG⊖/T…
Zadanie 1f
Solid ammonium chloride decomposes when heated to form two gases, ammonia and hydrogen chloride. (i) Write the chemical equation for this decomposition. (ii) Calculate the volume of ammonia produced at STP when an 8.00 g sample of ammonium chloride decomposes.…
Zadanie 17
A reaction has a negative ΔH and a negative ΔS. Which statement about the spontaneity of the reaction is correct? A. It is spontaneous at all temperatures B. It is spontaneous only at high temperatures C. It is spontaneous only at low…