The combustion of tristearin C57H110O6, a typical fat: 2C57H110O6 + 163O2 (g) -> 114 CO2(g) + 110 H2O(l) H = -75,520 kJ
On average, the metabolism of proteins produces ~ 4 Cal/g carbohydrates produces ~ 4Cal/g fats produces about ~ 9 Cal/g
(1 Cal = 1000 c
Calorimetry of Foods Most of the energy our bodies need comes from the metabolism of carbohydrates, fats and proteins.
Carbohydrates decompose into glucose, C6H12O6. Metabolism of glucose produces CO2 and H2O and energy C6H12O6(s) + 6O2 (g) -> 6CO2 (g) +
Problem When methylhydrazine, CH6N2, a rocket fuel, undergoes combustion the following reaction occurs: CH6N2(l) + 5 O2(g) -> 2N2(g) + 2CO2(g) + 6H2O(g) When 4.00 g of CH6N2(l) is combusted in a bomb calorimeter, the temperature of the calorimeter increas
Problem When 50.mL of 1.0M HCl and 50.mL of 1.0M NaOH are mixed in a calorimeter, the temperature of the resultant solution increases from 21.0oC to 27.5oC. Calculate the enthalpy change per mole of HCl for the reaction carried out at constant pressure, a
If two objects at different temperatures are in contact with one another, heat flows from the hotter body to the colder body in an attempt for the system to reach an equilibrium. Assuming that there is no heat lost to the surroundings, then: heat lost by
1st Law: E = q + w Work = - Pext V At constant volume, w = 0; E = qv At constant pressure, H = qp H > 0 endothermic H = E + RT ng Calorimetry: heat gained by colder object = heat lost by warmer object H < 0 exothermic
Problem: How much heat is needed to warm 250g (~ 1 cup) of water from 22oC to near its boiling point 98oC. The specific heat of water is 4.18 J/(g-K)?
q = m cs T q = (250g) (4.18 J/(g-K) (76K) = 7.9 x 104 J
Molar heat capacity, cP: amount of heat absorbed per mole of sample Molar heat capacity = cP = CP n Units of cP joule/(mole K) q = n cP T Specific heat capacity, cs: the amount of heat absorbed per unit mass of body specific heat capacity = cs = CP m Unit
Calorimetry Calorimetry is the measurement of the amount of heat flow and change in temperature accompanying a process. Heat capacity (at constant pressure), CP, of a body, is the amount of heat required to raise the temperature of the body by one degree
Relationship between H and E C(s) + 1/2 O2(g) -> CO(g) H = -110.5 kJ
Determine the change in internal energy accompanying this reaction. H = E + (PV) E = H - (PV) (PV) = (nRT) = RT(ng) E = H - RT(ng) or H = E + RTng
For this reaction ng = 0.5 mol; hence
Since w = - Pext V H = qp - Pext V + PextV = qp
For experiments carried out at constant volume, E is the quantity to use since changes in internal energy equal the amount of heat involved in the process.
However, chemical reactions are typically conducted
Enthalpy is defined as H = E + PV
For a system undergoing pressure-volume work, the change in enthalpy in the system is H = E + PV If the pressure is a constant external pressure, Pext, H = E + PextV From the 1st law: E = q + w For constant P: H = qp + w
Enthalpy and Internal Energy
We know that H = qp (at constant pressure) Since, E = q + w, if the volume is held constant, no pressurevolume work can be done on that system or by that system. work = - PextV = 0 at constant volume Hence, for constant volume
The enthalpy change for a reaction is equal in magnitude but opposite in sign to H for the reverse reaction CH4(g) + O2(g) -> CO2(g) + 2H2O(l) H = -890 kJ CO2(g) + 2H2O(l) -> CH4(g) + O2(g) H = +890 kJ
The enthalpy change for a reaction depends on the pha
The magnitude of H for a reaction is directly proportional to the amount of reactants consumed by the reaction. CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l) H = -890 kJ
Calculate the amount of heat that would be released when 4.50 g of CH4(g) is burned in an oxyge
In a chemical reaction, the enthalpy change during the reaction indicates whether the reaction releases energy or consumes energy. If H < 0, the reaction releases heat and is EXOTHERMIC If H > 0, the reaction absorbs heat and is ENDOTHERMIC
Enthalpy Most physical and chemical changes take place under the constant pressure of the Earth's atmosphere. The heat lost or gained by a system undergoing a process under constant pressure is related to the change in ENTHALPY (H) of the system H = Hfina
For a process which takes place at constant volume w = - Pext V = 0; if volume is constant E = q + w For constant volume processes, no work can be done E = qv where qv is the heat exchanged at constant volume
Like P, V, T, and n, E is a state function since the change in E depends only on the initial and final energies of the system and not on the details of the process the system underwent. However changes in q and w take place during the process and hence de
Sign convention The sign of E indicates whether the final energy is less than or more than the initial energy. The sign of E depends on relative magnitudes and signs of q and w If heat flows into the system Heat flows out of the system Work done by the sy
Energy Conservation and The First Law of Thermodynamics 1) Energy is conserved 2) Heat and work can produce equivalent effects 3) The only way that energy can be transferred is through heat and work. First Law E = q + w where E is the change in internal e
Energy, Work and Heat Heat exchange between the system and surrounding is one way of changing the energy of the system Work done by the system or on the system also changes the energy of the system. The energy of the system changes when the system undergo
Heat, and hence changes in energy, accompany almost all chemical reactions.
When a chemical reaction occurs by absorbing heat from its surroundings, the reaction is said to be ENDOTHERMIC.
When a chemical reaction is accompanied by the release of heat, th
Heat When the temperature of a system changes, the internal energy of the system changes. E = Ef - Ei If heat flows into the system, at constant volume, and there is no phase change, the temperature increases and E is positive.
If E is negative (at consta