4.4: energy in reactions Flashcards
what is an endothermic reaction?
an endothermic reaction is a reaction that absorbs heat from its surroundings, whereby the products have more energy than the reactants. Therefore, the enthalpy value is positive.
what is an exothermic reaction?
an exothermic reaction is a reaction that releases heat and hence, the products have less energy than the reactants and therefore, the enthalpy value is negative.
explain the process of dissolving ionic substances with regards to thermochemistry.
when ionic substances dissolve in water, the dissociation of ions requires energy and the hydration of ions releases energy. if more energy is required to disassociate the ions than what is released when ion-dipole interactions form, the reaction is endothermic. However, if less energy is required to dissociate the ions from the lattice than what is produced when the ion-dipole interactions form the reaction is exothermic.
how can the enthalpy of a solution be experimentally determined?
the enthalpy of a solution can be experimentally determined through a process known as calorimetry. The insulated apparatus, known as the calorimeter, measures the change of the temperature of the water and is hence, used to measure the energy released or absorbed by the reaction.
endothermic = cold feeling, absorbs heat and reduces temperature (e.g. cold pack)
exothermic = hot feeling, releases heat and increases temperature (e.g. hot pack)
random v systematic errors
random errors are human errors, that reduce the reliability and hence precisions of the results, can be caused by incorrect reading of the thermometer or inaccurate measurements.
systematic errors are errors that reduce the overall accuracy of the results, or how close they are to the accepted theoretical value. systematic errors can be a cause of incorrectly calibrated equipment or flawed experimental design.
