Chemical Energetics and Kinetics 211 Notes ⢠Thermodynamics ⢠The ...
Chemical Energetics and Kinetics 211 Notes
Thermodynamics The study of energy changes, quantitatively. Can answer questions such as: o What is the effect of a change in the parameter y on the property Z? o What is the position of equilibrium in a chemical reaction? Thermodynamics Is used to determine the position of equilibrium. It tells us nothing about how quickly equilibrium is achieved. Kinetics Is the study of how rapidly a reaction proceeds to equilibrium.
The Language of Thermodynamics System Any region of space being studied. Surroundings The remainder of the universe. Boundary The border, or wall, between the system and the surroundings. Diathermic Wall Heat is allowed to transfer between the system and surroundings. Adiabatic Wall No heat is allowed to transfer between the system and surroundings. Isolated System One that has no interactions with the surroundings (ie., no heat or matter transfer). Closed System No matter transfer to/from the surroundings. Open System Matter transfer is allowed between the system and surroundings.
State of a System o Defined by ascribing values to a sufficient number of variables, called state variables, to the system to make it reproducible. Such variables are macroscopic properties. o E.g., P, V, T, mass, composition, density, surface area, position in a gravitational field, degree of magnetisation. o Normally only specify the minimum number of variables to define the system. ∞ E.g., of T, p and density (p), only two are independent; no need to specify the third. Change of State Occurs when the value(s) of the independent state variables(s) defining the system are changed. Intensive Variable Independent of the mass of the system. Extensive Variable Directly proportional to the mass of a system. Process The path along which a change of state takes place. o Isochoric Process - Constant Volume. o Isothermal Process (Diathermic Process) - Constant Temperature. o Adiabatic Process - No heat exchange with surroundings. o Isobaric Process - Constant Pressure. o Iso-anything - Constant “anything”. Equilibrium o A system is said to be in equilibrium if it is stable with respect to an infinitesimal change. The properties of an isolated system at equilibrium do not change in time. Reversible Changes o Always proceed through a continuous series of equilibrium states. o
E.g. A change of pressure involving an ideal gas is reversible if the pressure is always equal to nRT/V.
o
In practice, a reversible process can only proceed infinitesimally slowly. However, we often approximate a process as being reversible if it occurs slowly enough.
Temperature o Temperature is a thermodynamic property used to measure the “hotness” of a system. o Observation has shown that heat transfers from the hotter to the colder body when they are in thermal contact. o Thermal contact allows for energy transfer without the exchange of matter. If no energy flow occurs between two systems in thermal contact, they are said to be in thermal equilibrium and are at the same temperature.
Extensive or Intensive Thermodynamic Property? Consider a system. Now, perform a thought experiment and divide the system in two. If the value of the variable does not change that variable is intensive. If the value changes, that variable is extensive. E.g. consider a beaker of water. The water is the system. The beaker is the boundary. Identify the following thermodynamic properties as extensive or intensive. o o o o o o o o o o
Temperature Mass Pressure Volume Concentration Density Refractive Index Enthalpy Entropy Heat Capacity
= Intensive = Extensive = Intensive = Extensive = Intensive = Intensive = Intensive = Extensive = Extensive = Extensive
Zeroth Law of Thermodynamics If two systems, A and B, are in thermal equilibrium with a third system, C, then they are also in thermal equilibrium with one another. The Zeroth Law may seem totally obvious, but it is an important concept that allows us to build a thermometer.
Thermodynamics Thermodynamics is the study of energy changes associated with a change of state. E.g. pressure change, melting, and chemical reaction. We measure energy changes by monitoring the amount of work done and/or the amount of heat transferred to/from a system.
Thermodynamics The study of energy changes, quantitatively. Can answer questions such as: o What is the effect of a change in the parameter y on the property Z? o What is the position of equilibrium in a chemical reaction? Thermodynamics Is used to determine the position of equilibrium. It tells us nothing about how quickly equilibrium is achieved. Kinetics Is the study of how rapidly a reaction proceeds to equilibrium.
The Language of Thermodynamics System Any region of space being studied. Surroundings The remainder of the universe. Boundary The border, or wall, between the system and the surroundings. Diathermic Wall Heat is allowed to transfer between the system and surroundings. Adiabatic Wall No heat is allowed to transfer between the system and surroundings. Isolated System One that has no interactions with the surroundings (ie., no heat or matter transfer). Closed System No matter transfer to/from the surroundings. Open System Matter transfer is allowed between the system and surroundings.
State of a System o Defined by ascribing values to a sufficient number of variables, called state variables, to the system to make it reproducible. Such variables are macroscopic properties. o E.g., P, V, T, mass, composition, density, surface area, position in a gravitational field, degree of magnetisation. o Normally only specify the minimum number of variables to define the system. ∞ E.g., of T, p and density (p), only two are independent; no need to specify the third. Change of State Occurs when the value(s) of the independent state variables(s) defining the system are changed. Intensive Variable Independent of the mass of the system. Extensive Variable Directly proportional to the mass of a system. Process The path along which a change of state takes place. o Isochoric Process - Constant Volume. o Isothermal Process (Diathermic Process) - Constant Temperature. o Adiabatic Process - No heat exchange with surroundings. o Isobaric Process - Constant Pressure. o Iso-anything - Constant “anything”. Equilibrium o A system is said to be in equilibrium if it is stable with respect to an infinitesimal change. The properties of an isolated system at equilibrium do not change in time. Reversible Changes o Always proceed through a continuous series of equilibrium states. o
E.g. A change of pressure involving an ideal gas is reversible if the pressure is always equal to nRT/V.
o
In practice, a reversible process can only proceed infinitesimally slowly. However, we often approximate a process as being reversible if it occurs slowly enough.
Temperature o Temperature is a thermodynamic property used to measure the “hotness” of a system. o Observation has shown that heat transfers from the hotter to the colder body when they are in thermal contact. o Thermal contact allows for energy transfer without the exchange of matter. If no energy flow occurs between two systems in thermal contact, they are said to be in thermal equilibrium and are at the same temperature.
Extensive or Intensive Thermodynamic Property? Consider a system. Now, perform a thought experiment and divide the system in two. If the value of the variable does not change that variable is intensive. If the value changes, that variable is extensive. E.g. consider a beaker of water. The water is the system. The beaker is the boundary. Identify the following thermodynamic properties as extensive or intensive. o o o o o o o o o o
Temperature Mass Pressure Volume Concentration Density Refractive Index Enthalpy Entropy Heat Capacity
= Intensive = Extensive = Intensive = Extensive = Intensive = Intensive = Intensive = Extensive = Extensive = Extensive
Zeroth Law of Thermodynamics If two systems, A and B, are in thermal equilibrium with a third system, C, then they are also in thermal equilibrium with one another. The Zeroth Law may seem totally obvious, but it is an important concept that allows us to build a thermometer.
Thermodynamics Thermodynamics is the study of energy changes associated with a change of state. E.g. pressure change, melting, and chemical reaction. We measure energy changes by monitoring the amount of work done and/or the amount of heat transferred to/from a system.
