Determine ΔH for the third reaction from the information given. C3H8(g) + 3 H2O(g) ↔ 3 CO(g) + 7 H2(g) ΔH = 499.0 kJ CO(g) + H2O(g) ↔ CO2(g) + H2(g) ΔH = -41.00 kJ C3H8(g) + 6 H2O(g) ↔ 3 CO2(g) + 10 H2 ΔH = ?
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
- Determine ΔH for the third reaction from the information given.
C3H8(g) + 3 H2O(g) ↔ 3 CO(g) + 7 H2(g) ΔH = 499.0 kJ
CO(g) + H2O(g) ↔ CO2(g) + H2(g) ΔH = -41.00 kJ
C3H8(g) + 6 H2O(g) ↔ 3 CO2(g) + 10 H2 ΔH = ?
Q2. How much heat (in kilojoules) is involved in the oxidation of 160.5 g of Fe at 25°C?
4 Fe(s) + 3 O 2(g)↔ 2 Fe 2O 3(l) --> ΔH = -1648 kJ
Q3. The specific heat capacity of Pt is 0.1328 J/g*°C. How many joules of heat are necessary to raise the temperature of 49.06 g of Pt from 25.0°C to 35.25 °C?
Q4. What is the sign of ΔH for the process of below?
I 2(l) → I 2(s)
A. positive and the process is endothermic
B. negative and the process is exothermic
C. positive and the process is exothermic
D. negative and the process is endothermic
Q5. The first step in the preparation of lead from galena, PbS, consists of roasting the ore in oxygen. The reaction is
2 PbS(s) + 3 O 2(g) ↔ 2 SO 2(g) + 2 PbO(s)
What is ΔH° rxn (in kilojoules)?
PbS(s) ΔH f o = -98.3 kJ/mol.
SO 2(g) ΔH f o = -296.8 kJ/mol.
PbO(s) ΔH f o = -219 kJ/mol.
Q6. What is the sign of ΔH for the process of below?
NaCl(l) → NaCl(g)
A. negative and the process is exothermic
B. positive and the process is exothermic
C. positive and the process is endothermic
D. negative and the process is endothermic
Q7. A simple method for the laboratory preparation of hydrogen involves reaction of zinc with hydrochloric acid;
Zn(s) + 2 HCl(aq) → ZnCl 2(aq) + H 2(g) ΔH = -152.5 kJ
How much heat in kilojoules is evolved if a total of 732.0 mL of H 2 was collected over water at 20.00 ° C and an atmospheric pressure of 338.8 mm Hg. The partial pressure of water at this temperature is 17.54 mm Hg? Assume heat evolved is directly proportional to the moles produced.
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