Calculate the change in internal energy of the following system: A balloon is cooled by removing 0.659 kJ of heat. It shrinks on cooling, and the atmosphere does 385 J of work on the balloon.

-310J

The change in internal energy (ΔE) of a system is the sum of the heat (Q) and work (W) done on or by the system. i.e

ΔE = Q + W       (i)

If heat is released by the system, Q is negative. Else it is positive.

If work is done on the system, W is positive. Else it is negative.

In this case, the system is the balloon and;

Q = -0.659kJ = -695J    [Q is negative because heat is removed from the system(balloon)]

W = +385J  [W is positive because work is done on the system (balloon)]

Substitute these values into equation (i) as follows;

ΔE = -695 + 385

ΔE = -310J

Therefore, the change in internal energy is -310J

PS: The negative value indicates that the system(balloon) has lost energy to its surrounding, thereby making the process exothermic.

a.   mass number from atomic number

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.