If the value of $C_{p}$ for nitrogen gas is $j K ^{-1} mol ^{-1}$, then the value of $\Delta H$ on heating $28 \,g$ of nitrogen gas from $0^{\circ} C$ to $100^{\circ} C$ at constant pressure will be :
- 1200 J
- 1300 J
- 1400 J
- 1500 J
The Correct Option is C
Solution and Explanation
$C_{p}=7 JK ^{-1} mol ^{-1}$
Weight of $N _{2}$ gas $=28\, gm$
$T_{1}=0^{\circ} C =273+0=273\, K$
$T_{2}=100^{\circ} C =273+100=373\, K$
Now, by using :
Number of moles
$=\frac{\text { Weight of } N _{2}}{\text { Molecular weight of } N _{2}}$
$=\frac{28}{14}=2$
Now, by using
$\Delta H = nCp (T_2 - T_1) $
$ = 2\times 7(373-273)$
$=14 \times 100=1400 \text { Joule }$
Top Questions on Enthalpy change
- The group 14 elements A and B have the first ionisation enthalpy values of 708 and 715 kJ mol$^{-1}$ respectively. The above values are lowest among their group members. The nature of their ions A$^{2+}$ and B$^{4+}$ respectively is:
- JEE Main - 2025
- Chemistry
- Enthalpy change
- The incorrect relationship in the following pairs in relation to ionisation enthalpies is:
- JEE Main - 2025
- Chemistry
- Enthalpy change
- Given below are two statements:
Statement (I): The radius of isoelectronic species increases in the order: \[ \text{Mg}^{2+} < \text{Na}^{+} < \text{F}^{-} < \text{O}^{2-} \] Statement (II): The magnitude of electron gain enthalpy of halogens decreases in the order: \[ \text{Cl} > \text{F} > \text{Br} > \text{I} \] In light of the above statements, choose the most appropriate answer from the options given below:- JEE Main - 2025
- Chemistry
- Enthalpy change
- Consider the following cases of standard enthalpy of reaction (\( \Delta H_f^\circ \) in kJ mol\(^{-1}\)): \[ \text{C}_2\text{H}_6(g) + 7 \text{O}_2(g) \rightarrow 2 \text{CO}_2(g) + 3 \text{H}_2\text{O}(l) \quad \Delta H_1^\circ = -1550 \] \[ \text{C(graphite)} + \text{O}_2(g) \rightarrow \text{CO}_2(g) \quad \Delta H_2^\circ = -393.5 \] \[ \text{H}_2(g) + \frac{1}{2} \text{O}_2(g) \rightarrow \text{H}_2\text{O}(g) \quad \Delta H_3^\circ = -286 \] The magnitude of \( \Delta H_f^\circ \) of \( \text{C}_2\text{H}_6(g) \) is \(\_\_\_\_\_\) kJ mol\(^{-1}\) (Nearest integer).
- JEE Main - 2025
- Chemistry
- Enthalpy change
- The bond dissociation energies of gaseous H2, Cl2, and HCl are 104, 58, and 103 kcal, respectively. The enthalpy of formation of HCl gas would be:
- BCECE - 2025
- Chemistry
- Enthalpy change
Questions Asked in WBJEE exam
What are the charges stored in the \( 1\,\mu\text{F} \) and \( 2\,\mu\text{F} \) capacitors in the circuit once current becomes steady?
- WBJEE - 2026
- Capacitors and Capacitance
Which one among the following compounds will most readily be dehydrated under acidic condition?
- WBJEE - 2026
- Organic Reactions
Manufacturers supply a zener diode with zener voltage \( V_z=5.6\,\text{V} \) and maximum power dissipation \( P_{\max}=\frac14\,\text{W} \). This zener diode is used in the circuit shown. Calculate the minimum value of the resistance \( R_s \) so that the zener diode will not burn when the input voltage is \( V_{in}=10\,\text{V} \).
- WBJEE - 2026
- Zener Diodes
Two charges \( +q \) and \( -q \) are placed at points \( A \) and \( B \) respectively which are at a distance \( 2L \) apart. \( C \) is the midpoint of \( AB \). The work done in moving a charge \( +Q \) along the semicircle CSD (\( W_1 \)) and along the line CBD (\( W_2 \)) are
- WBJEE - 2026
- electrostatic potential and capacitance
A piece of granite floats at the interface of mercury and water. If the densities of granite, water and mercury are \( \rho, \rho_1, \rho_2 \) respectively, the ratio of volume of granite in water to that in mercury is
- WBJEE - 2026
- Buoyancy and Floatation
Concepts Used:
Enthalpy change
Enthalpy Change refers to the difference between the heat content of the initial and final state of the reaction. Change in enthalpy can prove to be of great importance to find whether the reaction is exothermic or endothermic.
Formula for change in enthalpy is:-
dH = dU + d(PV)
The above equation can be written in the terms of initial and final states of the system which is defined below:
UF – UI = qP –p(VF – VI)
Or qP = (UF + pVF) – (UI + pVI)
Enthalpy (H) can be written as H= U + PV. Putting the value in the above equation, we obtained:
qP = HF – HI = ∆H
Hence, change in enthalpy ∆H = qP, referred to as the heat consumed at a constant pressure by the system. At constant pressure, we can also write,
∆H = ∆U + p∆V
Standard Enthalpy of Reaction
To specify the standard enthalpy of any reaction, it is calculated when all the components participating in the reaction i.e., the reactants and the products are in their standard form. Therefore the standard enthalpy of reaction is the enthalpy change that occurs in a system when a matter is transformed by a chemical reaction under standard conditions.