Thermochemical equations constant-pressure

When 0.113 g of benzene, C6H6, burns in excess oxygen in a calibrated constant-pressure calorimeter with a heat capacity of 551 J-(°C) I, the temperature of the calorimeter rises by 8.60°C. Write the thermochemical equation for... 

STRATEGY The heat released by the reaction at constant pressure is calculated from the temperature change multiplied by the heat capacity of the calorimeter. Use the molar mass of one species to convert the heat released into the reaction enthalpy corresponding to the thermochemical equation as written. If the temperature rises, the... 

Self-Test 6.11A When 0.231 g of phosphorus reacts with chlorine to form phosphorus trichloride, PC1 , in a constant-pressure calorimeter of heat capacity 216 J-(°C)1, the temperature of the calorimeter rises by 11.06°C. Write the thermochemical equation for the reaction. 

Whereas a lattice enthalpy is equal to the heat required (at constant pressure) to break up an ionic substance, a bond enthalpy is the heat required to break a specific type of bond at constant pressure. For example, the bond enthalpy of H2 is derived from the thermochemical equation... 

From this expression the value of the heat of reaction at constant pressure can be calculated if that at constant volume is known, or vice versa. An important use of equation (12.3) is in the determination of the AH values for combustion reactions, since the actual thermochemical measurements are made in an explosion bomb at constant volume. 

We now specify the equation of state used to model detonation products. For the ideal gas portion of the Helmholtz free energy, we use a polyatomic model including electronic, vibrational, and rotational states. Such a model can be conveniently expressed in terms of the heat of formation, standard entropy, and constant pressure heat capacity of each species. The heat capacities of many product species have been calculated by a direct sum over experimental electronic, vibrational, and rotational states. These calculations were performed to extend the heat capacity model beyond the 6000K upper limit used in the JANAF thermochemical tables (J. Phys. Chem. Ref. Data, Vol. 14, Suppl. 1, 1985). Chebyshev polynomials, which accurately reproduce heat capacities, were generated. 

When any substituent is introduced in hydrocarbon molecules to saturate double bond or triple bond, the electronic structure of molecule will be changed, thus the thermal effect of electron transfer of 1 mol atom will have some change. According to the impact of change in molecule structure, the explosion heat of explosive can be calculated based on the corresponding corrected thermochemical data of some groups and the corrected data are listed in Table 3.9. The combustion heat of CaHi,OcN compounds under constant pressure can be calculated as the following equation ... 

Analyze Our goal is to use a thermochemical equation to calculate the heat produced when a specific amount of methane gas is comhusted. According to Equation 5.18,890 kJ is released by the system when 1 mol CH4 is burned at constant pressure. 

Use thermochemical equations to relate the amount of heat energy transferred in reactions at constant pressure (AH) to the amount of substance involved in the reaction. (Section 5.4)... 

The complete combustion of ethanol, C2H50H(1), to form H20(g) and C02(g) at constant pressure releases 1235 kJ of heat per mole of C2H5OH. (a) Write a balanced thermochemical equation for this reaction, (b) Draw an enthalpy diagram for the reaction. 

Strategy Under constant-pressure conditions, the heat absorbed (qp) per mole of a reaction is given by AH. According to the thermochemical equation, 99.1 kJ of heat is given off (note the negative sign) for every mole of SO2 burned. To calculate the total amount of heat produced we first need to use the mass of SO2 given in the problem statement and the molar mass of SO2 to calculate the number of moles of SO2 reacted. 

According to this thermochemical equation, 2 moles of sodium react with 2 moles of water under constant-pressure conditions to produce 2 moles of aqueous NaOH, 1 mole of hydrogen gas, and 367.5 kJ of heat. Some of the energy produced by the reaction is used to do the work of pushing back a volume of air (V) against atmospheric pressure (P) (Figure 7.10), so the hydrogen gas can enter the atmosphere. 

Aqueous sodium hydrogen carbonate solution (baking soda solution) reacts with hydrochloric acid to produce aqueous sodium chloride, water, and carbon dioxide gas. The reaction absorbs 12.7 kJ of heat at constant pressure for each mole of sodium hydrogen carbonate. Write the thermochemical equation for the reaction. 

Consider the reaction of methane, CH4 (the principal constituent of natural gas), burning in oxygen at constant pressure. How much heat could you obtain from 10.0 g of methane, assuming you have an excess of oxygen You can answer this question if you know the enthalpy change for the reaction of 1 mol of methane. The thermochemical equation is... 

Reactions absorb or evolve definite quantities of heat under given conditions. At constant pressure, this heat of reaction is the enthalpy of reaction, AH. The chemical equation plus All for molar amounts of reactants is referred to as the thermochemical equation. With it, you can calculate the heat for any... 

When 1 mol of iron metal reacts with hydrochloric acid at constant temperature and pressure to produce hydrogen gas and aqueous iron(II) chloride, 89.1 kJ of heat evolves. Write a thermochemical equation for this reaction. 

What is the heat of reaction at constant pressure Use the following thermochemical equations ... 

Note that the sign of the lattice enthalpy must always be included in the thermochemical equation the reverse of lattice enthalpy is the heat energy released (at constant pressure) when one mole of ionic solid is formed from gaseous ions (Figure 15.5). 

This equation suggests that the Fe content of tetrahedrite-tennantite positively correlates with that of sphalerite at constant temperature and pressure, indicating Fe and Zn contends of tetrahedrite-tennantite are useful to estimate physicochemical parameters (/sj, /02 etc.) as well as Fe content of sphalerite, although detailed study on thermochemical properties of tennantite-tetrahedrite solid solution is still needed. 

Concerning the first field of application, the kinetics and equilibrium constants for several halide transfer reactions (equation 1) were measured in a pulsed electron high pressure mass spectrometer (HPMS)4 or in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR)5. From measurements of equilibrium constants performed at different temperatures, experimental values were obtained for the thermochemical quantities AG°, AH° and AS° for the reaction of equation 1. The heat of formation (AH°) of any carbocation of interest, R+, was then calculated from the AH0 of reaction and the AH° values of the other species (RC1, R Cl and R +) involved. 

A minor product (corresponding to about 0-5 % of the cyclopentene peak) was detected which had the same retention time as methylenecyclo-butane. At pressures below 3 mm the rate constant decreased with pressure and fell to approximately one half of the high-pressure value at 0-07 mm. The results obtained could be fitted by the Kassel equation by assuming that the reactant had eighteen effective oscillators. The data are thus consistent with the isomerization being a truly unimolecular transformation. On the basis both of the observed energy of activation and thermochemical data and of estimates of bond strengths, these... 

For the sake of illustration we have calculated the equilibrium composition of a mixture, formed by decomposition of methane with steam at an initial ratio of 1 2 moles, 900 K and in the 10 to 1000 atm range. Thermochemical data for CH4, H2O, H2, CO will be found in Example 10, for CO2 in Example 11. The calculation was performed according to relations (6.96) — (6.102), constants of the Beattie-Bridgman equation are given in Appendix 11 for the individual pure constituents. The results are plotted in Fig. 24. It will be seen from the plot, that for all constituents 900 K is a high enough temperature for deviations from ideal behaviour to become apparent only at elevated pressure. 

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