Advertisements
Advertisements
Question
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
Solution
Given: Given equations are,
2H3BO3(aq) → B2O3(s) + 3H2O(l), ΔrH° = + 14.4 kJ ...(i)
H3BO3(aq) → HBO2(aq) + H2O(l), ΔrH° = - 0.02 kJ ....(ii)
H2B4O7(s) → 2B2O3(s) + H2O(l), ΔrH° = + 17.3 kJ .....(iii)
To find: The standard enthalpy of the given reaction (ΔrH°)
Calculation:
Reverse equation (i) and multiply by 2,
2B2O3(s) + 6H2O(l) → 4H3BO3(aq) , ΔrH° = - 28.8 kJ ......(iv)
Multiply equation (ii) by 4
4H3BO3(aq) → 4HBO2(aq) + 4H2O(l), ΔrH° = - 0.08 kJ .......(v)
Add equations (iv), (v) and (iii),
2B2O3(s) + 6H2O(l) → 4H3BO3(aq) , ΔrH° = - 28.8 kJ
4H3BO3(aq) → 4HBO2(aq) + 4H2O(l), ΔrH° = - 0.08 kJ
H2B4O7(s) → 2B2O3(s) + H2O(l), ΔrH° = + 17.3 kJ
_____________________________________________________
H2B4O7(s) + H2O(l) → 4HBO2(aq) ΔrH° = - 28.8 + (- 0.08) + 17.3 = - 11.58 kJ
The standard enthalpy (ΔrH°) of the given reaction is -11.58 kJ.
APPEARS IN
RELATED QUESTIONS
Answer the following in one or two sentences.
What is standard state of a substance?
Answer in brief.
How will you calculate reaction enthalpy from data on bond enthalpies?
Answer in brief.
What is the standard enthalpy of combustion? Give an example.
Answer the following question.
State Hess’s law of constant heat summation. Illustrate with an example. State its applications.
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]
Calculate the standard enthalpy of formation of liquid methanol from the following data:
- \[\ce{CH3OH_{(l)} + \frac{3}{2} O_{2(g)} -> CO_{2(g)} + 2H2O_{(l)}}\] ∆H° = – 726 kJ mol–1
- \[\ce{C_{(Graphite)} + O_{2(g)} -> CO_{2(g)}}\] ∆cH° = – 393 kJ mol–1
- \[\ce{H_{2(g)} + \frac{1}{2} O_{2(g)} -> H2O_{(l)}}\] ∆fH° = – 286 kJ mol–1
Define the Bond enthalpy.
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 for CCl4(g), H2O(g), CO2(g), and HCl(g) are −25.5, −57.8, −94.1 and −22.1 kcal mol−1, respectively.
∆H for the reaction
\[\ce{CCl4_{(g)} + 2H2O_{(g)} -> CO2_{(g)} + 4HCl_{(g)}}\] at 298 K
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 ____________.
\[\ce{S + 3/2O2 -> SO3 +2{x} kcal}\] .........(i)
\[\ce{SO2 + 1/2O2 -> SO3 + {y} kcal}\] .......(ii)
The heat of formation of SO2 is ____________.
Enthalpy of formation of two compounds x and y are −84 kJ and −156 kJ respectively. Which of the following statements is CORRECT?
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.
Calculate the standard enthalpy of formation of CH3OH(l) from the following data:
- \[\ce{CH3OH_{(l)} + 3/2 O2_{(g)} -> CO2_{(g)} + 2H2O_{(l)}ΔH^° = - 726 kJ mol^{-1}}\]
- \[\ce{C_{(s)} + O2_{(g)} → CO2_{(g)}Δ_cH^° = – 393 kJ mol^{-1}}\]
- \[\ce{H2_{(g)} + 1/2 O2_{(g)} -> H2O_{(l)}Δ_fH^° = - 286 kJ mol^{-1}}\]
\[\ce{A -> B}\], ∆H = −10 kJ mol−1, Ea(f) = 50 kJ mol−1, then Ea of \[\ce{B -> A}\] will be ______.
What is enthalpy of formation of NH3 if bond enthalpies as (N ≡ N) = - 941 kJ/mol.
\[\ce{(H - H)}\] = 436 kJ/mol and \[\ce{(N - H)}\] = 389 kJ/mol?
When 0.5 gram of sulphur is burnt to form SO2, 4.6 kJ of heat liberated. Calculate enthalpy of formation of SO2(g). (Atomic mass : S = 32, O = 16)
Calculate the standard enthalpy of the reaction:
SiO2(s) + 3C(graphite) → SiC(s) + 2CO(g) from the following reactions:
- Si(s) + O2(g) → SiO2(s), ΔrH° = −911kJ
- 2C(graphite) + O2(g) → 2CO(g), ΔrH° = −221kJ
- Si(s) + C(graphite) → SiC(s), ΔrH° = −65.3kJ
Standard enthalpy of combustion of a substance is given. Then Write thermochemical equation.
ΔcH0[CH3CHO(l)] = - 1166 kJ mol-1
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.
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.
The heat evolved in the combustion of 6.022 x 1021 carbon particles is 3.94 kJ. The heat of combustion of carbon is ______.
Calculate heat evolved for combustion of 13 gm of acetylene (C2H2).
Given: \[\ce{C2H2_{(g)} + 5/2O_{2(g)}-> 2CO_{2(g)} + H2O_{(l)} \Delta_{(c)}H^{0} = - 1300 kJ}\]
Calculate the standard enthalpy of combustion of methane if the standard enthalpy of formation of methane, carbon dioxide and water are −74.8, −393.5 and −285.8 kJmol−1 respectively.
