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Define the Bond enthalpy. - Chemistry

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प्रश्न

Define the Bond enthalpy.

परिभाषा

उत्तर

The enthalpy change required to break a particular covalent bond in one mole of the gaseous molecule to produce gaseous atoms and/or radicals is called bond enthalpy.

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Thermochemistry
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अध्याय 4: Chemical Thermodynamics - Long answer questions

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एससीईआरटी महाराष्ट्र Chemistry [English] 12 Standard HSC
अध्याय 4 Chemical Thermodynamics
Long answer questions | Q 2.1

संबंधित प्रश्न

Answer the following in one or two sentences.

What is standard state of a substance?


Answer in brief.

What is the standard enthalpy of combustion? Give an example.


Answer in brief.

How much heat is evolved when 12 g of CO reacts with NO2? The reaction is:

4CO(g)  2NO2(g) → 4CO2(g) + N2(g), ΔrH° = - 1200 kJ


Answer the following question.

Calculate ΔrH° for the following reaction at 298 K:

1) 2H3BO3(aq) → B2O3(s) + 3H2O(l), ΔrH° = + 14.4 kJ

2) H3BO3(aq) → HBO2(aq) + H2O(l), ΔrH° = - 0.02 kJ

3) H2B4O7(s) → 2B2O3(s) + H2O(l), ΔrH° = + 17.3 kJ


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.


The enthalpy change of the following reaction:

\[\ce{CH_{4(g)} + Cl_{2(g)} -> CH3Cl_{(g)} + HCl_{(g)}ΔH^0 = –104 kJ}\]

Calculate C – Cl bond enthalpy. The bond enthalpies are:

Bond C − H Cl − Cl H − Cl
∆H°/kJ mol−1 414 243 431

Define standard enthalpy of formation.


Calculate the standard enthalpy of formation of liquid methanol from the following data:

  1. \[\ce{CH3OH_{(l)} + \frac{3}{2} O_{2(g)} -> CO_{2(g)} + 2H2O_{(l)}}\]     ∆H° = – 726 kJ mol–1
  2. \[\ce{C_{(Graphite)} + O_{2(g)} -> CO_{2(g)}}\]          ∆cH° = – 393 kJ mol–1
  3. \[\ce{H_{2(g)} + \frac{1}{2} O_{2(g)} -> H2O_{(l)}}\]          ∆fH° = – 286 kJ mol–1 

Calculate the standard enthalpy of the reaction.

\[\ce{2Fe_{(s)} + \frac{3}{2} O_{2(g)} -> Fe2O_{3(s)}}\]

Given:

1. \[\ce{2Al_{(s)} + Fe2O_{3(s)} -> 2Fe_{(s)} + Al_2O_{3(s)}}\], rH° = –847.6 kJ
2. \[\ce{2Al_{(s)} + \frac{3}{2} O_{2(g)} -> Al2O_{3(s)}}\], rH° = –1670 kJ

Define the Enthalpy of ionisation.


Classify the following into intensive and extensive properties.

Pressure, volume, mass, temperature.


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 ____________.


The enthalpy of formation of nitrogen dioxide is +33.2 kJ mol−1. The enthalpy of the reaction \[\ce{2N2_{(g)} + 4O2_{(g)} -> 4NO2_{(g)}}\]; is ____________.


Given that,

\[\ce{C_{(s)} + O_{2(g)} -> CO_{2(g)}}\]   ΔH° = -X kJ

\[\ce{2CO_{(g)} + O_{2(g)} -> 2CO_{2(g)}}\]   ΔH° = - Y kJ, then standard enthalpy of formation of carbon monoxide is ________.


Calculate the standard enthalpy of formation of CH3OH(l) from the following data:

  1. \[\ce{CH3OH_{(l)} + 3/2 O2_{(g)} -> CO2_{(g)} + 2H2O_{(l)}ΔH^° = - 726 kJ mol^{-1}}\]
  2. \[\ce{C_{(s)} + O2_{(g)} → CO2_{(g)}Δ_cH^° = – 393 kJ mol^{-1}}\]
  3. \[\ce{H2_{(g)} + 1/2 O2_{(g)} -> H2O_{(l)}Δ_fH^° = - 286 kJ mol^{-1}}\]

Identify the invalid equation.


\[\ce{A -> B}\], ∆H = −10 kJ mol−1, Ea(f) = 50 kJ mol−1, then Ea of \[\ce{B -> A}\] will be ______.


Calculate the standard enthalpy of the reaction:

SiO2(s) + 3C(graphite) → SiC(s) + 2CO(g) from the following reactions:

  1. Si(s) + O2(g) → SiO2(s), ΔrH° = −911kJ
  2. 2C(graphite) + O2(g) → 2CO(g), Δr = −221kJ
  3. Si(s) + C(graphite) → SiC(s), Δr = −65.3kJ

Standard enthalpy of combustion of a substance is given. Then Write thermochemical equation.

ΔcH0[CH3CHO(l)] = - 1166 kJ mol-1


The enthalpy of combustion of S (rhombic) is − 297 kJ mo1-1. Calculate the amount of sulphur required to produce 29. 74 kJ of heat.


Calculate heat evolved for combustion of 13 gm of acetylene (C2H2).

Given: \[\ce{C2H2_{(g)} + 5/2O_{2(g)}-> 2CO_{2(g)} + H2O_{(l)} \Delta_{(c)}H^{0} = - 1300 kJ}\]


Heat of combustion of CH4(g) is -890 kJ/mole. What is the value of Δc H of 8gm of methane?


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