Hess' Law

Q.

Calculate the enthalpy of the following reaction. $H_{2}C=C{H}_2\left(g\right)+H_2\left(g\right)\to C{H}_3-C{H}_3\left(g\right)$

The bond energies of C - H, C - C, C = C & H - H are 99, 83, 147 & 104 Kcal respectively.

1. 30 K cal

2. -30 K cal

3. 20 K cal

4. -20 K cal

Q. Calculate the $△$H of the reaction

$H-\underset{\stackrel{|}{Cl}}{\stackrel{\underset{|}{H}}{C}}-Cl\left(g\right)⟶C\left(s\right)+2H\left(g\right)+2Cl\left(g\right)$

Bond energy for C-H bond & C-Cl bond are 415KJ and 326KJ respectively.

1. -1482 kJ

2. 1482 kJ

3. 1483 kJ

4. -1483 kJ

Q. Determine the heat of transformation of C(diamond)→ C(graphite) from the following data.

$C_{\left(diamond\right)}+O_2\left(g\right)\to C{O}_2\left(g\right)△H=-94.5Kcal$

$C_{\left(graphite\right)}+O_2\left(g\right)\to C{O}_2\left(g\right)△H=-94.0Kcal$

1. 0.5 K cal

2. -0.5 K cal

3. -188.5 K cal

4. 188.5 K cal

Q. Calculate the reasonance energy of $N_{2}O$ from the following data.of $△H_f^o$ $N_{2}O=82kJmo{l}^{-1}$

Bond energy of N $\equiv$ N, N = N, O = O and N = O bonds are 946, 418, 498 & 607 $kJmo{l}^{-1}$ respectively.

1. 80 kJ

2. 90 KJ

3. 88 kJ

4. 85 kJ

Q. Hess's law of constant heat summation in based on

1. Conservation of mass
2. $E=m{c}^2$
3. First law of thermodynamics
4. None of the above

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

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

Q.

Given the bond energies $N\equiv N$, $H-H$ and $N-H$ bonds are $945,436$ and $391kJmol{e}^{-1}$ respectively, the enthalpy of the following reaction $N_2\left(g\right)+3H_2\left(g\right)\to 2N{H}_3\left(g\right)$ is

1. 102 kJ

2. 90 kJ

3. 105 kJ

4. -93 kJ

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. +250 kJ

4. -125 kJ

Q.

The molar entropies of $HI\left(g\right),H\left(g\right)$ and $I\left(g\right)$ at $298K$ are $206.5,114.6$, and $180.7Jmol{e}^{-1}{K}^{-1}$ respectively. Using the $\Delta G^0$ given below, Calculate the bond energy of HI.

$H\left(g\right)\to H\left(g\right)+I\left(g\right)$; $\Delta G^0=271.8kJ$

1. 282.4 kj/mole

2. 298.3 kJ/mole

3. 100 kJ/mole

4. 32.17kJ/mole

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. −174.5

2. −139.6

3. −180.75

4. −69.8