Enthalpy of Combustion

Q. The heat of combustion of carbon to $C{O}_2$ is -393.5 kJ/mol. The heat released upon formation of 35.2g of $C{O}_2$ from carbon and oxygen gas is

1. -630 kJ
2. -3.15 kJ
3. -315 kJ
4. +315 kJ

Q.

10ml of gaseous Hydrocarbon on combustion gives 40ml of CO₂ gas and 50ml H₂O (Vapour). The Hydrocarbon is______.

1. C₄H₅

2. C₄H₈

3. C₄H₁₀

4. C₈H₁₀

Q. The heat of formation of $CO$ and $C{O}_2$ are $-26.4$ kcal and $-94$ kcal respectively. The heat of combustion of carbon monoxide will be:

1. $+26.4$ kcal
2. $-67.6$ kcal
3. $-120.4$ kcal
4. $+52.8$ kcal

Q.

When 5 litres of a gas mixture of methane and propane is perfectly combusted at $0^{\circ }C$ and 1 atmosphere, 16 litres of oxygen at the same temperature and pressure is consumed. The amount of heat released from this combustion is

$kJ\left(\Delta H_{comb.}\right(C{H}_4)=890kJmo{l}^{-1},\Delta H_{comb.}(C_3{H}_8)=2220kJmo{l}^{-1})$ is

1. 38
2. 32
3. 317
4. 477

Q. The heats of combustion of carbon and carbon monoxide are –393.5 and –283.5 $kJ{mol}^{-1}$ respectively. The
heat of formation (in kJ) of carbon monoxide per mole is:

1. 676.5
2. - 676.5
3. - 110.5
4. 110.5

Q.

$\Delta U^{\theta }$ of combustion of methane is $–XkJmo{l}^{-1}$. The value of $\Delta H^{\theta }$ is

(i) $=\Delta U^{\theta }$
(ii) $>\Delta U^{\theta }$
(iii) $<\Delta U^{\theta }$
(iv) $=0$

Q.

The standard enthalpy of formation of octane (C₈H₁₈) is −250 kJ/mol. Calculate the enthalpy of combustion of C₈H_18.
Given : enthalpy of formation of CO₂(g) and H₂O(l) are −394 kJ/mol and −286 kJ/mol respectively:

1. −5726 kJ/mol
2. −5476 kJ/mol
3. −5200 kJ/mol
4. −5310 kJ/mol

Q. The heat of combustion of benzene in a bomb calorimeter (i.e., constant volume) was found to be $3263.9kJmo{l}^{-1}$ at ${25}^{o}C$. Calculate the heat of combustion of benzene at constant pressure.

1. $-4767.6kJmo{l}^{-1}$
2. $3667.6kJmo{l}^{-1}$
3. $2767.6kJmo{l}^{-1}$
4. $-3267.6kJmo{l}^{-1}$

Q. When a certain amount of ethylene was combusted, $6226\text{kJ}$ heat was evolved. If heat of combustion of $1$ mole of ethylene is $1411\text{kJ}$, the volume of $O_2$ (at NTP) that entered into the reaction is:

1. $296.5\text{mL}$
2. $296.5\text{litres}$
3. $6226\times 22.4\text{litres}$
4. $22.4\text{litres}$

Q. The enthalpy of combustion of propane, graphite and dihydrogen at $298K\text{are}–2220.0{\text{kJ mol}}^{–1},–393.5{\text{kJ mol}}^{–1}\text{and}–285.8{\text{kJ mol}}^{–1}$ respectively.
The magnitude of enthalpy of formation of propane
$\left(C_3{H}_8\right)$ is ~\text{ kJ mol}^{–1}\). (Nearest integer)

Q. Value of f $K_p$ for the equilibrium reaction

$N_2{O}_{4\left(g\right)}\rightleftharpoons 2N{O}_{2\left(g\right)}$ at 288 K is 47.9. The $K_C$ for this reaction at same temperature is ........(Nearest integer)

$(R=0.083Lbar{K}^{-1}mo{l}^{-1})$

Q. The equilibrium constant for the reaction at $298K$ is:
Given that: $\Delta H^o=-29.8kJmo{l}^{-1}\Delta S^o=-0.100kJ{K}^{-1}mo{l}^{-1}$

1. $1.0\times {10}^{10}$

2. $1.0\times {10}^{-10}$

3. 10
4. 1

Q. Which of the following statement is correct?

1. More the number of carbon atoms, lesser is the heat of combustion.
2. All of the above.
3. More the heat of combustion, lesser is the stability of alkenes.
4. More the heat of hydrogenation, more is the stability of alkenes.

Q. (i) Cis - 2 - butene $\to$ trans-2-butene, $△H_1$
(ii) Cis - 2 - butene $\to$ 1 - butene, $△H_2$
(iii) Trans-2-butene is more stable than cis - 2 - butene.
(iv) Enthalpy of combustion of 1 - butene, $△H=-649.8kcal/mol$
(v) $9△H_1+5△H_2=0$
(vi) Enthalpy of combustion of trans 2 - butene, $△H=-647.0kcal/mol.$

The value of $△H_1$ and $△H_2$ in kcal/mol are

1. 1.8, -1.0
2. -5, 9
3. -2, 3.6
4. - 1.0, 1.8

Q. The standard enthalpy of combustion at ${25}^{o}C$ of hydrogen, cyclohexene ($C_6{H}_{10}$) and cyclohexane ($C_6{H}_{12}$ ) are $-241,-3800and-3920kJmo{l}^{-1}$ respectively. Calculate the heat of hydrogenation of cyclohexene ( in $kJmo{l}^{-1}$)

1. $-121$
2. $+121$
3. $+221$
4. $-221$

Q.

10ml of mixture of CO, CH_{​​​​​4} and N_{​​​​​​2} exploded with excess of oxygen gave a contraction of 6.5ml.There was a further contraction of 7 ml when the residual gas was treated with KOH.What is the amount of CH_{​​​​​4} in the original mixture?

Q. The standard heat of combustion of solid boron is equal to:

1. $△H_f^o\left(B_2{O}_3\right)$
2. $3/2△H_f^o\left(B_2{O}_3\right)$
3. $2△H_f^o\left(B_2{O}_3\right)$
4. $1/2△H_f^o\left(B_2{O}_3\right)$

Q. If liquids A and B form an ideal solution

1. The Gibbs free energy as well as the enthalpy of mixing are each zero
2. The entropy of mixing is zero
3. The Gibbs free energy as well as the entropy of mixing are each zero
4. The enthalpy of mixing is zero

Q. The energy of combustion of propane $\left(C_3{H}_8\right)$ gas in terms of given data is:
Bond energy (kJ/mol)
$$\begin{array}{ccccc}{ϵ}_{C-H}& {ϵ}_{O=O}& {ϵ}_{C=O}& {ϵ}_{O-H}& {ϵ}_{C-C}\\ +x_1& +x_2& +x_3& +x_4& +x_5\end{array}$$
Resonance energy of $C{O}_2$ is $-zkJ/mol$ and $△H_{vaporization}\left[H_{2}O\right]isykJ/mol$

1. $8x_1+2x_5+5x_2-6x_3-8x_4-4y-3z$
2. $6x_1+x_5+5x_2-3x_3-4x_4-4y-3z$
3. $8x_1+2x_5+5x_2-6x_3-8x_4-y-z$
4. $8x_1+2x_5+5x_2-6x_3-8x_4+4y+3z$

Q.

Calculate the efficiency of a fuel cell given the heat of combustion of hydrogen is -286.0 kJ Mol^-1 , and the Gibbs free energy change for the fuel cell is -238 kJ mol^-1

1. 63.%

2. 73%

3. 83%

4. 41.5%

Q. The combustion of hydrogen-oxygen mixture is used to produce very high temperatures $(\approx {2500}^{o}C)$ needed for certain types of welding operations.
$H_2\left(g\right)+\frac{1}{2}{O}_2\left(g\right)\to H_{2}O\left(g\right);△H=-230.9kJ$
Quantity of heat, (in kJ) evolved when a 200 g mixture containing equal parts of $H_2$ and $O_2$ by mass is burned, is

1. $1.44\times {10}^{3}kJ$
2. $2.72\times {10}^{3}kJ$
3. $4.3524\times {10}^{4}kJ$
4. $1.36\times {10}^{3}kJ$

Q. The heat of formation of $CO$ and $C{O}_2$ are $-26.4$ kcal and $-94$ kcal respectively. The heat of combustion of carbon monoxide will be:

1. $-120.4$ kcal
2. $+26.4$ kcal
3. $-67.6$ kcal
4. $+52.8$ kcal

Q.

∆U° of combustion of CH4 (g)at certain temperature is -393kj/ mol.Then value of ∆H° is

1)0

2)<∆U°

3)>∆U°

4)=∆U°

Q.

What happens if the entropy decreases ?

Q. Which of the following statement is correct regarding the heat of combustion of combustible substances?

1. It is always an exothermic reaction
2. Its value does not change with temperature
3. It may be exothermic as well as endothermic
4. It is applicable to gaseous substances only

Q.

A gas mixture $3.67L$ in volume contains $C_2{H}_4$ and $C{H}_4$ is proportion of $2:1$ by moles and is at ${25}^{\circ }C$ and $1atm$. If the $\Delta H_C$ ($C_2{H}_4)$ and $\Delta H_C$ $\left(C{H}_4\right)$ are $-1400$ and $-900kJ/mol$ find heat evolved on burning this mixture

1. 20.91 kJ

2. 50.88 kJ

3. 185 kJ

4. 160 kJ

Q. Using the data (all value are in kilocalorie per mole at ${25}^{\circ }C$ ) given below, the bond energy of $C-C$ and bond $C-H$ bond is $mkcal$ and $nkcal$, respectively. Calculate the value of $m+n$
$\Delta H_{\text{combustion~of~ethane}}^{\circ }=-372.0\Delta H_{\text{Combustion of propane}}^{\circ }=-530.0\Delta H^{\circ }for{C}_{\text{(graphite)}}\to C\left(g\right)=+172.0\text{Bond energy of H - H bond}=+104.0\Delta H_f^{\circ }of{H}_{2}O\left(l\right)=-68.0\Delta H_f^{\circ }ofC{O}_2\left(g\right)=-94.0$

Q. For the reversible reaction, $A+2B\to 3C$, if equilibrium constant is $1\times {10}^2$ at 27°C then the value of $\Delta r{G}^{\circ }$ at the same temperature will be:
$(R=2cal{K}^{-1}mo{l}^{-1})$

1. $-8.21kcalmo{l}^{-1}$
2. $-2.76kcalmo{l}^{-1}$
3. $-4.31kcalmo{l}^{-1}$
4. $12.27kcalmo{l}^{-1}$

Q. Enthalpy of is always exothermic.

1. formation
2. combustion
3. solution
4. neutralisation

Q. The heat liberated on complete combustion of $7.8g$ benzene is $327kJ$. This heat was measured at constant volume and at ${27}^{o}C$. Calculate the heat of combustion of benzene at constant pressure.

1. $-3270kJmo{l}^{-1}$
2. $-3274kJmo{l}^{-1}$
3. $-1637kJmo{l}^{-1}$
4. None of the above