"qrxn" typically represents the heat transferred during a chemical reaction.
The relationship between qrxn (heat of reaction) and qsur (heat of surrounding) is described by the first law of thermodynamics, which states that the heat released or absorbed by a reaction is equal and opposite to the heat gained or lost by the surrounding environment. In an exothermic reaction, qrxn is negative and qsur is positive as heat is released to the surroundings. In an endothermic reaction, qrxn is positive and qsur is negative as heat is absorbed from the surroundings.
The amount of heat generated or absorbed in a chemical reaction can be studied using a calorimeter. our chemical reaction) is placed in a well-insulated vessel surrounded by water (surroundings). A thermometer is used to measure the heat transferred to or from the system to the surroundings. The heat that the chemical reaction puts out, or takes up, (qrxn) is simply the moles of the limiting reagent, nlimiting reagent times ΔHrxn. qrxn = nlimiting reagent·ΔH