Unit 6: Thermodynamics

According to the College Board, "The laws of thermodynamics describe the essential role of energy and explain and predict the direction of changes in matter🧊💧. The availability or disposition of energy plays a role in virtually all observed chemical processes. Thermodynamics provides tools for understanding this key role, particularly the conservation of energy, including energy transfer in the forms of heat and work. Chemical bonding is central🔑 to chemistry.

Matter can undergo physical and chemical changes. Such energy changes are related to temperature changes🌡️. This can easily be seen with the melting of ice:

Enthalpy, or heat energy, is represented by ΔH (Δ is the delta sign, which means change). If there is a negative change in energy, or -ΔH, an exothermic reaction is taking place and energy is released🔥 from the system to the surroundings. If there is a positive change in energy, or +ΔH, an endothermic reaction is taking place and energy is absorbed into the system from the surroundings.

Temperature reflects the average kinetic energy, or random motion, of particles. Kinetic energy is speed, so as temperature increases, molecules collide with the walls of the container faster.

The absolute enthalpy of a system (H) cannot be measured directly. However, it is possible to measure changes in enthalpy (ΔH) by measuring temperature changes, which represent heat being lost or gained. To measure enthalpy changes, we use what is called calorimetry.

Phase changes could be represented in a variety of ways! The following curves might help you understand the relation between phase changes and endothermic/exothermic processes more.

Enthalpy is a thermodynamic quantity equivalent to the total heat content of a system. Basically, enthalpy helps describe heat energy within a system and how this heat energy moves through, in, and out of a system🔄. However, as we've previously discussed, you cannot measure absolute enthalpy, but rather you can only measure changes in enthalpy, or ΔH.

While it may not seem so, bonds contain energy😲. When you think about why some reactions are exothermic and others are endothermic, it is because of the breaking and forming of bonds! There is a general rule here, and that is: BREAKING BONDS REQUIRES ENERGY & MAKING BONDS RELEASES ENERGY.

The standard enthalpy of formation (ΔHf) or standard heat of formation of a compound is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements in their most stable state at standard conditions (25°C and 1atm). Essentially, it is the amount of energy it takes to form a compound.

A pathway is the route that a process takes. Typically, pathway dependency/independency is applied to functions. Essentially, if the result of something depends on the order in which you did it, it is pathway dependent and if it is not, it is pathway independent.