Question

6. A sample of ammonium chloride dissolves in water, absorbing heat from the surrounding water and causing the temperature to drop by 20 °C. If the heat change for the reaction is +300 J, what is the heat change for the surrounding water?

Answer 1

Q6. Heat change for reaction = 300 J

According to energy conservation principle, energy is neither created nor destroyed but converted from one form to another.

Heat change for reaction + heat change for water = 0

heat change for water = -(Heat change for reaction)

heat change for water = -(300 )

heat change for water = -300 J

(negative sign indicates water loses heat)

Q12. Given :

Change in internal energy, $\Delta$ U = -400 kJ

(negative sign indicates energy is released)

Work done, w = -250 kJ

(negative sign indicates work is done by the system)

According to first law of thermodynamics,

$\Delta$U = q + w

where q = heat change of system

Substituting the values of $\Delta$ U and w

-400 kJ = q + (-250 kJ)

q = -400 kJ + 250 kJ

q = -150 kJ

(negative sign indicates heat is released)

Amount of energy released as heat = 150 kJ