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प्रश्न
Answer the following in one or two sentences.
What is standard state of a substance?
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उत्तर
- The standard state of a substance is the form in which the substance is most stable at a pressure of 1 bar and at a temperature of 298 K.
- If the reaction involves species in solution, its standard state is 1 M concentration.
e.g. Standard states of certain elements and compounds are (at 1 bar and 25 °C); \[\ce{H2_{(g)}, Hg_{(l)}, Na_{(s)}, C_{(graphite)}, C2H5OH_{(l)}, CaCO3_{(s)}, CO2_{(g)}, C2H5OH_{(l)}, H2O_{(l)}, CaCO3_{(s)}, CO2_{(g)}}\].
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संबंधित प्रश्न
Select the most appropriate option.
Which of the following reactions is exothermic?
Calculate the total heat required
a) to melt 180 g of ice at 0 °C
b) heat it to 100 °C and then
c) vapourise it at that temperature.
[Given: ΔfusH° (ice) = 6.01 kJ mol-1 at 0 °C, ΔvapH° (H2O) = 40.7 kJ mol-1 at 100 °C, Specific heat of water is 4.18 J g-1 K-1]
The enthalpy change for the reaction, \[\ce{C2H4_{(g)} + H2_{(g)} -> C2H6_{(g)}}\] is −620 J when 100 mL of ethylene and 100 ml of \[\ce{H2}\] react at 1 bar pressure. Calculate the pressure volume type of work and ΔU for the reaction.
Calculate enthalpy of formation of HCl if bond enthalpies of H2, Cl2 and HCl are 434 kJ mol-1, 242 kJ mol–1 and 431 kJ mol–1 respectively.
Define standard enthalpy of formation.
Write an application of Hess’s law.
When 2 moles of C2H6(g) are completely burnt, 3129 kJ of heat is liberated. If ∆Hf for CO2(g) and H2O(l) are −395 and −286 kJ per mole respectively, the heat combustion of C2H6(g) is ____________.
The volume of oxygen required for complete combustion of 0.25 mole of methane at STP is ______.
When 6.0 g of graphite reacts with dihydrogen to give methane gas, 37.4 kJ of heat is liberated. What is standard enthalpy of formation of CH4 (g)?
The heat of formations of CO(g) and CO2(g) are −26.4 kcal and −94.0 kcal respectively. The heat of combustion of carbon monoxide will be ____________.
The standard heats of formation in kcal mol−1 of NO2(g) and N2O4(g) are 8.0 and 2.0 respectively. The heat of dimerization of NO2 in kcal is ____________.
\[\ce{2NO2_{(g)} ⇌ N2O4_{(g)}}\]
The enthalpy change accompanying a reaction in which 1 mole of the substance in the standard state reacts completely with oxygen or is completely burnt is called as ____________.
Given the reaction,
\[\ce{CH2O_{(g)} + O2_{(g)} -> CO2_{(g)} + H2O_{(g)}}\] ΔH = −527 kJ
How much heat will be evolved in the formation of 60 g of CO2?
Calculate the enthalpy of hydrogenation of C2H4(g), given that the enthalpy of formation of ethane and ethylene are −30.2 kcal and +12.5 kcal respectively.
Standard enthalpy of formation of water is - 286 kJ mol-1. When 1800 mg of water is formed from its constituent elements in their standard states the amount of energy liberated is ______.
An ideal gas expands isothermally and reversibly from 10 m3 to 20 m3 at 300 K performing 5 .187 kJ of work on surrounding. Calculate number of moles of gas undergoing expansion. (R = 8.314 J K-1 mol-1)
Heat of formation of water is - 272 kJ mol-1. What quantity of water is converted to H2 and O2 by 750 kJ of heat?
Standard entropies of N2(g), H2(g), and NH3(g) are a1, a2 and a3 J K-1 mol-1 respectively. What is value of ΔS° for formation of NH3(g)?
Which of the following equations has ΔfH° and ΔH° same?
Heat of formation of ethane, ethylene acetylene and carbon dioxide are - 136, - 66, - 228 and - 395 (all in kJ) respectively, most stable among them is ______.
From the following bond energies:
H – H bond energy: 431.37 kJ mol−1
C = C bond energy: 606.10 kJ mol−1
C – C bond energy: 336.49 kJ mol−1
C – H bond energy: 410.50 kJ mol−1
Enthalpy for the given reaction will be:
\[\begin{array}{cc}
\phantom{}\ce{H}\phantom{...}\ce{H}\phantom{...................}\ce{H}\phantom{...}\ce{H}\phantom{....}\\
\phantom{.}|\phantom{....}|\phantom{....................}|\phantom{....}|\phantom{.....}\\
\ce{C = C + H - H -> H - C - C - H}\\
\phantom{.}|\phantom{....}|\phantom{....................}|\phantom{....}|\phantom{.....}\\
\phantom{}\ce{H}\phantom{...}\ce{H}\phantom{...................}\ce{H}\phantom{...}\ce{H}\phantom{....}
\end{array}\]
Calculate the standard enthalpy of the reaction, \[\ce{SiO2_{(s)} + 3C_{(graphite)} -> SiC_{(s)} + 2CO_{(g)}}\] from the following reactions:
- \[\ce{Si_{(s)} + O2_{(g)} -> SiO2_{(s)}}\], ΔrH0 = −911 kJ
- \[\ce{2C_{(graphite)} + O2_{(g)} -> 2CO_{(g)}}\], ΔrH0 = −221 kJ
- \[\ce{Si_{(s)} + C_{(graphite)} -> SiC_{(s)}}\], ΔrH0 = −65.3 kJ
Standard enthalpy of combustion of a substance is given. Then Write thermochemical equation.
ΔcH0[C2H5OH(1)] = - 1409 kJ mol-1
Heat of combustion of methane is - 890 kJ/mol. On combustion of 12 gm of methane in excess of oxygen, ______ heat is evolved.
For the reaction, aA + bB → cC + dD, write the expression for enthalpy change of reaction in terms of enthalpies of formation of reactants and products.
For the reaction, H2 + I2 ⇌ 2HI; ΔH = 12.4 kcal. The heat of formation of HI, ΔHf = ______.
Calculate ΔsubH of the H2O from the given data:
\[\ce{H2O_{(s)}->H2O_{(l)},}\] ΔfusH = 6.01kJ mol−1
\[\ce{H2O_{(l)}-> H2O_{(g)},}\] ΔVapH = 45.07 kJ mol−1.
Heat of combustion of CH4(g) is -890 kJ/mole. What is the value of Δc H of 8gm of methane?
