A balloon filled with helium (32°C and 1.7 atm) bursts. Immediately afterwards the expansion of helium can be considered as:

We first recall the basic form of the First Law of Thermodynamics, which is written as

$$\Delta U \;=\; Q \;-\; W,$$

where $$\Delta U$$ is the change in internal energy of the system, $$Q$$ is the heat supplied to the system, and $$W$$ is the work done by the system on the surroundings.

Now consider what actually happens the moment a rubber balloon filled with helium suddenly bursts. The rubber skin tears so quickly that the gas inside finds itself in the open atmosphere almost instantaneously. Because the time interval of the tearing is extremely small, there is practically no opportunity for energy to flow as heat between the helium and the surrounding air. In thermodynamics, a process in which $$Q = 0$$ is called adiabatic. Substituting $$Q = 0$$ into the First Law gives

$$\Delta U \;=\; -W.$$

Next, let us decide whether the work term represents a reversible or an irreversible process. In a reversible expansion every intermediate state is in mechanical equilibrium, so the external pressure $$P_{\text{ext}}$$ always matches the internal pressure $$P_{\text{int}}$$ infinitesimally closely, and the system passes through well-defined equilibrium states. In the bursting of a balloon the internal pressure, initially $$1.7\ \text{atm}$$, is suddenly released against an external pressure of roughly $$1\ \text{atm}$$. That large pressure difference means the gas expands in one violent “jump,” far from equilibrium. Because the expansion occurs against a finite pressure difference, it cannot trace a sequence of equilibrium states, so it is by definition irreversible.

Putting the two observations together:

• Heat exchange: $$Q = 0 \;\Rightarrow\;$$ adiabatic.
• Mechanical path: large pressure difference, single rapid step $$\Rightarrow$$ irreversible.

Therefore the expansion of helium immediately after the balloon bursts is best described as an irreversible adiabatic process.

Hence, the correct answer is Option B.