Define enthalpy change and discuss its signific... - SS1 Chemistry Energy Changes in Chemical Reactions Question

Enthalpy change is the heat energy exchanged during a chemical reaction at constant pressure. It represents the difference in enthalpy (H) between the products and the reactants and is denoted as ΔH. Enthalpy change is significant as it provides information about the heat absorbed or released during a reaction and helps determine the overall energy change of the system.

 

In an exothermic reaction, the products have lower enthalpy than the reactants, resulting in a negative ΔH value. This indicates that the reaction releases heat energy to the surroundings. For example, the combustion of methane (CH4) is an exothermic reaction with a negative enthalpy change. It releases heat and is commonly used for heating or cooking purposes.

 

In an endothermic reaction, the products have higher enthalpy than the reactants, resulting in a positive ΔH value. This indicates that the reaction absorbs heat energy from the surroundings. An example of an endothermic reaction is the process of photosynthesis in plants, where carbon dioxide (CO2) and water (H2O) react in the presence of sunlight to produce glucose and oxygen. This reaction requires energy input in the form of sunlight to proceed.

 

Enthalpy change is related to the heat absorbed or released during a reaction through the equation ΔH = q, where q represents the heat exchanged between the system and the surroundings. For an exothermic reaction, q is negative, indicating that heat is released by the system. For an endothermic reaction, q is positive, indicating that heat is absorbed by the system.

 

Calorimetry is a technique used to measure enthalpy changes experimentally. It involves the use of a calorimeter, a device that can accurately measure the heat exchanged during a reaction. By measuring the temperature change of a known mass of a substance (often water) surrounding the reaction, the heat released or absorbed can be determined. Calorimetry allows for the determination of enthalpy changes in a wide range of reactions and is an essential tool in studying thermodynamics.