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Thermodynamics Thermochemistry System and Surroundings The part of the universe under study or investigation is called the system while the rest of the universe that may exchange energy and matter with the system is called the surroundings The universe is the sum of the system and surroundings Types of Systems Systems can be further classified into three categories Open System where there is a complete transfer of mass and energy from system to surroundings Closed System where only energy transfer occurs between system and surroundings Isolated System where there is no transfer of mass or energy between system and surroundings Examples Open system examples include a cup of tea or an air conditioning system Closed system examples include a pressure cooker or a diathermic container where heat transfer occurs Isolated system examples are rare and typically theoretical Systems and Boundaries in Thermodynamics In thermodynamics systems are classified into three types open closed and isolated An open system involves the transfer of both mass and energy a closed system involves only the transfer of energy and an isolated system involves neither mass nor energy exchange Types of Boundaries A boundary is a line or area that separates a system from its surrounding environment Boundaries can be real or imaginary rigid or flexible and diathermic or adiabatic Real or Imaginary A real boundary is visible such as in a closed container while an imaginary boundary is created in the mind such as the uppermost layer of a liquid in an open container Rigid or Flexible A rigid boundary is solid and cannot be changed while a flexible boundary can be expanded or compressed such as with a piston in an open container Diathermic or Adiabatic A diathermic boundary allows for the transfer of heat while an adiabatic boundary does not Understanding Types of Systems and Properties A system can be open closed or isolated A closed system is rigid in nature and has boundaries such as real or imaginary rigid or flexible diathermic or adiabatic Extensive properties depend on the mass of substance while intensive properties do not Examples of extensive properties are area volume heat capacity energy and mass Examples of intensive properties are pressure temperature specific heat capacity viscosity molarity molality normality pH density and mole fraction Rules to Identify Extensive and Intensive Properties When two extensive properties are divided an intensive property is formed Extensive properties are additive while intensive properties are not In thermodynamics properties can be classified into extensive and intensive properties Extensive properties are additive in nature meaning that they increase as the size or amount of the system increases Examples include mass and volume Intensive properties are not additive and do not depend on the size or amount of the system Examples include temperature and pressure Molarity normality density and mole fraction are examples of properties that can be either extensive or intensive depending on the context State functions are properties that only depend on the initial and final state of the system while path functions depend on the path taken between those states Examples of state functions include pressure volume and temperature while examples of path functions include heat and work In an isothermal process the temperature remains constant and the relationship between pressure and volume is described by Boyle s law p1v1 p2v2 In an isobaric process the pressure remains constant and the relationship between volume and temperature is described by Charles s law v1 t1 v2 t2 Thermodynamic Processes and Graphs In thermodynamics pressure is often kept constant while observing a graph between pressure and volume This gives rise to the isobaric process where pressure remains constant and volume can change Similarly in the isochoric process volume is kept constant and pressure can change The adiabatic process involves no heat exchange while the cyclic process starts and ends at the same point forming a cycle Combining these processes we can obtain graphs that represent them In an examination students may be asked to identify which of the given lines represent each of the processes Isobaric Pressure is kept constant and volume increases Isothermal Temperature is kept constant Adiabatic No heat exchange occurs Isochoric Volume is kept constant Reversible and irreversible processes differ in terms of their time to completion with reversible being slower and taking infinite time to complete Reversible processes occur in small steps and are in equilibrium with the previous step while irreversible processes occur in a single step with no equilibrium in between Heat Heat is a form of energy and is a path function meaning it depends on the path taken and not just the initial and final points Its unit is joule Understanding Heat in Chemistry In chemistry heat is classified into two categories heat given to the system and heat given by the system Heat given to the system is considered positive while heat given by the system is negative When given a numerical question it is important to determine whether heat is being given to or by the system to correctly calculate the value Heat Capacity Heat capacity refers to the amount of heat required to raise the temperature of a system by one degree Celsius There are two types of heat capacity specific heat capacity and molar heat capacity Specific heat capacity is the amount of heat required to raise the temperature of one gram of a substance while molar heat capacity is the amount of heat required to raise the temperature of one mole of a substan ce Specific Heat Capacity The formula for specific heat capacity is q m t where q is the amount of heat m is the mass of the substance and t is the change in temperature Molar Heat Capacity The formula for molar heat capacity is q n t where q is the amount of heat n is the number of moles of the substance and t is the change in temperature The relationship between specific heat capacity and molar heat capacity is Cp m Cp gram and Cv m Cv gram Work is the force applied to an object multiplied by the distance the object displaces in the direction of the force Pressure volume work is calculated by determining the expansion or compression of a gas in a piston system If the pressure of the gas is greater than the external pressure the volume will increase resulting in expansion If the external pressure is greater

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UA CHEM 380 - Thermodynamics & Thermochemistry

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