Hess' Law

Q. The enthalpy change for a reaction $N_2\left(g\right)+3H_2\left(g\right)\to 2N{H}_3\left(g\right)$ is -92.2 kJ/mol. Calculate the enthalpy of formation of ammonia.

1. -92.2 kJ/mol
2. -46.1 kJ/mol
3. 46.1 kJ/mol
4. -92.2 kJ/mol

Q. Hess' law is used

1. When a directly measured enthalpy change of reaction is not available
2. To calculate an enthalpy change value through multiple steps.
3. Because enthalpy is a state function.
4. All of these options are correct

Q.

If at 298 K the bond energies of C - H, C - C, C=C and H - H bonds are respectively 414, 347, 615 and 435 kJ $mo{l}^{-1}$, the value of enthalpy change for the reaction
$C{H}_2=C{H}_2\left(g\right)+H_2\left(g\right)\to C{H}_3-C{H}_3$ is:

1. -250 kJ

2. +125 kJ

3. -125 kJ

4. +250 kJ

Q. Hess' law is applicable for determination of enthalpy of

1. Reaction
2. Formation
3. Transition
4. All of the above

Q. How many steps are involved in Born Haber cycle for sodium chloride?

1. 4
2. 5
3. 6
4. 7

Q. If the enthalpy of hydrogenation of $C_6{H}_6\left(l\right)$ into $C_6{H}_{12}\left(l\right)$ is - 205 kJ and the resonance energy of $C_6{H}_6\left(l\right)$ is -152 kJ/mol then the enthalpy of hydrogenation of cyclohexene is: (Assume $\Delta H_{vap}$ of $C_6{H}_6\left(l\right),C_6{H}_8\left(l\right),C_6{H}_{12}\left(l\right)$ all are equal).

1. $-535.5\text{kJ/mol}$
2. $-238\text{kJ/mol}$
3. $-357\text{kJ/mol}$
4. $-119\text{kJ/mol}$

Q. The lattice energy of solid KCl is $181{\text{kcalmol}}^{-1}$ and the enthalpy of solution of $KCl$ in $H_{2}O$ is $1.0{\text{kcalmol}}^{-1}$. If the hydration enthalpies of $K^{+}$ and $C{l}^{-}$ ions are in the ratio of 2:1, then the enthalpy of hydration of $K^{+}$ is $-x{\text{kcalmol}}^{-1}$. Find the value of $x$.

Q. Assertion: Born Haber cycle is based on Hess's law.
Reason: Lattice enthalpy can be calculate by Born- Haber cycle.

1. Both assertion and reason are true and reason is the correct explanation of the assertion

2. Both assertion and reason are true but reason is not the correct explanation of the assertion

3. Assertion is true but reason is false

4. Assertion and reason both are false

Q. Hess law is applicable for the determination of heat of

1. Reaction
2. Formation
3. Transition
4. All of these

Q.

$C\left(s\right)+O_2\left(g\right)\to C{O}_2\left(g\right),{\Delta }_{r}H=-94.3kcal/mol$

$CO\left(g\right)+\frac{1}{2}{O}_2\left(g\right)\to C{O}_2\left(g\right),{\Delta }_{r}H=-67.4kcal/mol$

$O_2\left(g\right)\to 2O\left(g\right),{\Delta }_{r}H=117.4Kcal/mol$

$CO\left(g\right)\to C\left(g\right)+O\left(g\right),{\Delta }_{r}H=230.6Kcal/mol$

Calculate: ${\Delta }_{r}HforC\left(s\right)\to C\left(g\right)inKcal/mol$

1. $165kcal/mol$

2. $145kcal/mol$

3. $185kcal/mol$

4. $205kcal/mol$

Q.

The standard heat of formation values of $S{F}_6\left(g\right)$ , $S\left(g\right)$ and $F\left(g\right)$ are: $-1100,275$ and $80KJmo{l}^{-1}$ respectively. Then the average S - F bond energy in $S{F}_6$ is:

1. $301KJmo{l}^{-1}$

2. $-183KJmo{l}^{-1}$

3. $309KJmo{l}^{-1}$

4. $280KJmo{l}^{-1}$

Q.

Consider the reaction:

$4N{O}_2\left(g\right)+O_2\left(g\right)\to 2N_2{O}_5\left(g\right),{\Delta }_{r}H=-111kJ$. If $N_2{O}_5\left(s\right)$ is formed instead of $N_2{O}_5\left(g\right)$ in the above reaction, the ${\Delta }_{r}H$ value will be:

(given, $\Delta H$ of sublimation for $N_2{O}_5$ is $54kJmo{l}^{-1}$)

1. + 54 kJ
2. + 219 kJ
3. − 219 J
4. −165 kJ

Q. If for
(i) $C+O_2\to C{O}_2$ (ii) $C+\frac{1}{2}{O}_2\to CO$ (iii) $CO+\frac{1}{2}{O}_2\to C{O}_2$
The heat of reaction are Q, – 12 and – 10 $kJ/mol$ respectively. Then Q =

1. – 2
2. 2
3. – 22
4. – 16

Q. $2Fe\left(s\right)+\frac{3}{2}{O}_2\left(g\right)\to F{e}_2{O}_3\left(s\right)(△H=-193.4kJ)......\left(1\right)$
$Mg\left(s\right)+\frac{1}{2}{O}_2\left(g\right)\to MgO\left(s\right)(△H=-140.2kJ)......\left(2\right)$

What is $△$∆H of the reaction? $3Mg+F{e}_2{O}_3\to 3MgO+2Fe$

1. -272.3 kJ

2. 272.3 kJ

3. 272.2 kJ

4. -227.2 kJ

Q.

Consider the reaction:

$4N{O}_2\left(g\right)+O_2\left(g\right)\to 2N_2{O}_5\left(g\right),{\Delta }_{r}H=-111kJ$. If $N_2{O}_5\left(s\right)$ is formed instead of $N_2{O}_5\left(g\right)$ in the above reaction, the ${\Delta }_{r}H$ value will be:

(given, $\Delta H$ of sublimation for $N_2{O}_5$ is $54kJmo{l}^{-1}$)

1. + 54 kJ
2. + 219 kJ
3. − 219 J
4. −165 kJ

Q.

Ethyl chloride $\left(C_2{H}_{5}Cl\right)$, is prepared by reaction of ethylene with hydrogen chloride :

$C_2{H}_4\left(g\right)+HCl\left(g\right)\to C_2{H}_{5}Cl\left(g\right)\Delta H=-72.3kJ$. What is the value of $\Delta E$ (in KJ), if 70g of ethylene and 73g of $HCl$ are allowed to react at 300K?

1. −69.8

2. −180.75

3. −174.5

4. −139.6

Q.

Polymerisation of ethene to poly - ethene is represented by the equation
$n(C{H}_2=C{H}_2)\to (-C{H}_2-C{H}_2-{)}_n$
Given that average enthalpies of C = C and C - C bonds at 298 K are 590 and 331 kJ $mo{l}^{-1}$ respectively, predict the enthalpy change when 56g of ethene changes to polyethylene.

1. 72 kJ

2. -72 kJ

3. 144 kJ

4. -144 kJ