Identify whether the following processes are exothermic or...

Identify whether the following processes are exothermic or endothermic. Is the sign on $q_{\mathrm{sys}}$ positive or negative? (a) the reaction of $\mathrm{Na}(\mathrm{s})$ and $\mathrm{Cl}_{2}(\mathrm{g})$ (b) cooling and condensing gaseous $\mathrm{N}_{2}$ to form liquid $\mathrm{N}_{2}$ (c) cooling a soft drink from $25^{\circ} \mathrm{C}$ to $0^{\circ} \mathrm{C}$ (d) heating $\mathrm{HgO}$ (s) to form $\mathrm{Hg}(\ell)$ and $\mathrm{O}_{2}(\mathrm{g})$

Identify whether the following processes are exothermic or endothermic. Is the sign on $q_{\mathrm{sys}}$ positive or negative?
(a) the reaction of $\mathrm{Na}(\mathrm{s})$ and $\mathrm{Cl}_{2}(\mathrm{g})$
(b) cooling and condensing gaseous $\mathrm{N}_{2}$ to form liquid $\mathrm{N}_{2}$
(c) cooling a soft drink from $25^{\circ} \mathrm{C}$ to $0^{\circ} \mathrm{C}$
(d) heating $\mathrm{HgO}$ (s) to form $\mathrm{Hg}(\ell)$ and $\mathrm{O}_{2}(\mathrm{g})$

Key Concepts

Exothermic Process

An exothermic process is one in which energy is released to the surroundings, typically in the form of heat. In such processes, the system loses energy, and the value of q (heat) for the system is negative. This release of energy usually results in an increase in the temperature of the surroundings.

Endothermic Process

An endothermic process absorbs energy from its surroundings, usually as heat. In these processes, the system gains energy, and consequently the value of q for the system is positive. This absorption of heat typically leads to a decrease in the temperature of the surroundings.

Heat Flow Sign Convention

The sign convention for heat, represented by q, is crucial in thermodynamics. When heat is released from the system to the surroundings, q is negative, indicating that the system is losing energy. Conversely, when heat is absorbed by the system from the surroundings, q is positive, indicating energy gain by the system.

Thermodynamic System and Surroundings

In thermodynamics, distinguishing between the system and its surroundings is essential for understanding energy transfer mechanisms. The system is the part of the universe that is under study, and the surroundings are everything outside of it. The direction of heat flow—whether energy is entering or leaving the system—is key to determining the thermodynamic characteristics of the process.

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