First law; internal energy, work and heat — NEET & JEE Questions

Question 1 · difficulty L1 · recall

Using the chemistry sign convention, the first law of thermodynamics is commonly written as

• A. $\Delta U=q+w$
• B. $\Delta U=q-w$ always
• C. $\Delta U=qw$
• D. $\Delta U=q/w$

Question 2 · difficulty L2 · understanding

A sample of n -octane $(1.14 \mathrm{~g})$ was completely burnt in excess of oxygen in a bomb calorimeter, whose heat capacity is $5 \mathrm{~kJ} \mathrm{~K}^{-1}$. As a result of combustion reaction, the temperature of the calorimeter is increased by 5 K . The magnitude of the heat of combustion of octane at constant volume is__________ $\mathrm{kJ} \mathrm{mol}^{-1}$ (nearest integer).

Question 3 · difficulty L2 · understanding

Three moles of an ideal gas are compressed isothermally from $$60 \mathrm{~L}$$ to $$20 \mathrm{~L}$$ using constant pressure of $$5 \mathrm{~atm}$$. Heat exchange $$\mathrm{Q}$$ for the compression is - _________ Lit. atm.

Question 4 · difficulty L2 · understanding

If 5 moles of an ideal gas expands from $$10 \mathrm{~L}$$ to a volume of $$100 \mathrm{~L}$$ at $$300 \mathrm{~K}$$ under isothermal and reversible condition then work, $$\mathrm{w}$$, is $$-x \mathrm{~J}$$. The value of $$x$$ is __________. (Given R = 8.314 J K$$^{-1}$$ mol$$^{-1}$$)

Question 5 · difficulty L2 · understanding

When a $$60 \mathrm{~W}$$ electric heater is immersed in a gas for 100 s in a constant volume container with adiabatic walls, the temperature of the gas rises by $$5^{\circ} \mathrm{C}$$. The heat capacity of the given gas is ___________ $$\mathrm{J} \mathrm{K}^{-1}$$ (Nearest integer)

Question 6 · difficulty L2 · understanding

1 mole of ideal gas is allowed to expand reversibly and adiabatically from a temperature of $27^{\circ} \mathrm{C}$. The work done is $3 \mathrm{~kJ} \mathrm{~mol}^{-1}$. The final temperature of the gas is ________ $\mathrm{K}$ (Nearest integer). Given $\mathrm{C_V}=20 \mathrm{~J} \mathrm{~mol}^{-1} \mathrm{~K}^{-1}$

Question 7 · difficulty L2 · understanding

When 2 litre of ideal gas expands isothermally into vacuum to a total volume of 6 litre, the change in internal energy is ____________ J. (Nearest integer)

Question 8 · difficulty L2 · understanding

A gas (Molar mass = 280 $$\mathrm{~g} \mathrm{~mol}^{-1}$$) was burnt in excess $$\mathrm{O}_{2}$$ in a constant volume calorimeter and during combustion the temperature of calorimeter increased from $$298.0 \mathrm{~K}$$ to $$298.45$$ $$\mathrm{K}$$. If the heat capacity of calorimeter is $$2.5 \mathrm{~kJ} \mathrm{~K}^{-1}$$ and enthalpy of combustion of gas is $$9 \mathrm{~kJ} \mathrm{~mol}^{-1}$$ then amount of gas burnt is _____________ g. (Nearest Integer)

Question 9 · difficulty L2 · understanding

4.0 L of an ideal gas is allowed to expand isothermally into vacuum until the total volume is 2.0 L. The amount of heat absorbed in this expansion is ____________ L atm.

Question 10 · difficulty L2 · understanding

A system does 200 J of work and at the same time absorbs 150 J of heat. The magnitude of the change in internal energy is ____________ J. (Nearest integer)