GENCHEM 2 4TH Q

• Thermochemistry – the study of energy or heat flow that accompanies a chemical reaction and/or physical transformation.
• Heat is a form of energy transfer between two objects as a result of their difference in temperature.
• System is the part of the universe being studied
• surroundings include everything else in the universe.
• Heat will always flow spontaneously from an area of higher temperature to an area of lower temperature.
• An open system can exchange both matter and energy with its surroundings.
• A closed system can exchange energy but not matter with its surroundings.
• An isolated system exchanges neither energy nor matter with the surroundings.
• Exothermic = releases energy
• Endothermic = absorbs energy
• First Law of Thermodynamics “states that the energy of the universe is constant.”
• Law of Conservation of Energy “energy is neither created nor destroyed, it can only be transferred between the system and the surroundings.”
• System gains heat = +q
• System loses heat = -q
• Work done on the system = +W
• Work done by the system = -W
• In thermochemistry, the units used in the change of energy are: J (joules) kJ (kilojoules)
• 1 kJ = 1000 J
• 1 calorie = 4.184 J
• 1 Calorie = 1 kcal = 1000 calories
• calorie (c) must not be confused with the food calorie (C)
• Heat capacity – the amount of energy required to raise the temperature of the sample by 1℃
• Specific Heat – the energy required to raise 1 gram of a substance by 1℃.
• The flow of energy (as heat) between the system and its surroundings is measured through calorimetry.
• A calorimeter is an insulator apparatus that contains water or any liquid of known heat capacity.
• A chemical equation that shows the value and direction of heat involved in a reaction is specifically called thermochemical equation.
• Enthalpy (H) is the amount of heat absorbed or released by a chemical reaction at constant atmospheric pressure in the form of chemical energy.
• Enthalpy of a reaction (∆𝑯) is the difference between the enthalpy of the products and the reactants
• Enthalpy is an extensive property. The magnitude is proportional to the amount of reactants and products in the reaction.
• The standard molar enthalpy of formation (∆𝐻° 𝑓) of a compound is the change in enthalpy when the compound is formed from its elements under standard conditions
• The enthalpy of formation for an element in its elemental state or naturally occurring state will always be zero because it takes no energy to form a naturally occurring compound.
• Hess’ law “The enthalpy of a sum of a series of reactions is equal to the sum of enthalpies of those two reactions
• The spontaneity of a process refers to how it occurs on its own without the help of any external factor
• Spontaneity only tells whether a reaction will occur or not but will not predict the rate of a process
• According to the Thomsen-Berthelot principle:
• Randomness also influences spontaneity
• Spontaneous processes occur from an ordered state to a more random arrangement.
• Entropy is a measure of molecular randomness.
• Third law of Thermodynamics “states that a perfectly ordered pure crystalline solid at zero Kelvin will have a zero entropy
• Chemical reactions that produce higher number of product particles than that of reactant particles are usually spontaneous