Energy heat change

Chemical reactions are a source of energy because the energy of chemical bonds can be converted to heat, light, or electrical energy. Heat changes can be measured by calorimetry. 

T. W. Richards, The Significance of Changing Atomic Volume 111. The Relation of Changing Heat Capacity to Change of Free Energy. Heat of Reaction. Change of Volume, and Chemical Affinity". Z. Physik. Chem. 42. 129-154 (1902). 

Thermoanalytical techniques such as differential scanning calorimetry (DSC) and thermogravi-metric analysis (TGA) have also been widely used to study rubber oxidation [24—27]. The oxidative stability of mbbers and the effectiveness of various antioxidants can be evaluated with DSC based on the heat change (oxidation exotherm) during oxidation, the activation energy of oxidation, the isothermal induction time, the onset temperamre of oxidation, and the oxidation peak temperature. 

Instantaneous heat transfer requirements may be determined by recognizing that the thermal energy input must be used either to effect a sensible heat change or the reaction. If q is the heat transfer rate,... 

Sensible heat change = energy gain by heat transfer through walls + energy effect accompanying reaction... 

Sometimes, the unknown quantity in the cycle is the lattice energy, U. From the cycle just shown, we know that the heat change is the same regardless of the pathway by which NaCl(s) is formed. Therefore, we see that... 

But we can now be more specific. The internal energy U changes in response to two variables, work w and heat energy q, as defined by... 

Many of the reactions that chemists study are reactions that occur at constant pressure. During the discussion of the coffee-cup calorimeter, the heat change at constant temperature was defined as qp. Because this constant-pressure situation is so common in chemistry, a special thermodynamic term is used to describe this energy enthalpy. The enthalpy change, AH, is equal to the heat gained or lost by the system under constant-pressure conditions. The following sign conventions apply ... 

From the definition of the heat of reaction, Qp will depend on the temperature T at which the reaction and product enthalpies are evaluated. The heat of reaction at one temperature T0 can be related to that at another temperature 7. Consider the reaction configuration shown in Fig. 1.1. According to the First Faw of Thermodynamics, the heat changes that proceed from reactants at temperature T() to products at temperature 7), by either path A or path B must be the same. Path A raises the reactants from temperature T0 to 7, and reacts at 7). Path B reacts at T0 and raises the products from T0 to 7). This energy equality, which relates the heats of reaction at the two different temperatures, is written as... 

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