Thermodynamics BCH 341 lecture 3

Thermodynamics is the study of the patterns of energy change. Thermodynamics is the study of the patterns of energy change. Thermo means energy Thermo means energy Dynamics means Patterns of change Dynamics means Patterns of change BCH 341 lecture 3

Thermodynamics deals with: Thermodynamics deals with: a) energy a) energy b) The stability of molecules and direction of change. b) The stability of molecules and direction of change. BCH 341 lecture 3

Examples: Imagine a brick resting on window ledge 3 meters high. As the brick rests on the ledge it has potential energy. Imagine a brick resting on window ledge 3 meters high. As the brick rests on the ledge it has potential energy. If you knock the brick out of the ledge, the potential energy is converted to kinetic energy( the brick accelerated towards the ground). If you knock the brick out of the ledge, the potential energy is converted to kinetic energy( the brick accelerated towards the ground). When the brick hits the ground the kinetic energy converted to light energy (sparks), Sound energy and chemical energy (the brick breaks). When the brick hits the ground the kinetic energy converted to light energy (sparks), Sound energy and chemical energy (the brick breaks). BCH 341 lecture 3

To study thermodynamics we will introduce two new terms which are: To study thermodynamics we will introduce two new terms which are: 1- The system 2- The surroundings BCH 341 lecture 3

Two types of exchange can occur between the system and surroundings. Two types of exchange can occur between the system and surroundings. 1- Energy exchange (heat, radiation….etc). 2-Matter exchange (movement of molecules across the boundary between the system and the surroundings). BCH 341 lecture 3

Based on the types of exchange which take place, three types of systems are identified. Based on the types of exchange which take place, three types of systems are identified. 1- Isolated systems: no exchange of matter or energy. 2-Open systems: Exchange of both matter and energy. 3- Closed system: no exchange of matter but exchange of energy. BCH 341 lecture 3

The total energy of a system before the process has taken place, called the initial state. The total energy of a system before the process has taken place, called the initial state. While the total energy of a system after the process has taken place, called final state. While the total energy of a system after the process has taken place, called final state. The equilibrium state is that condition in which no further change is occurring within the system or between the system and its surroundings. The equilibrium state is that condition in which no further change is occurring within the system or between the system and its surroundings. BCH 341 lecture 3

Thermodynamic process are either: Thermodynamic process are either: -Reversible: happens slow enough to be reversed -Irreversible: can not be reserved BCH 341 lecture 3

The first law of thermodynamics Energy can be exchanged between the system and its surroundings. Energy can be exchanged between the system and its surroundings. But the total energy of the system + the surrounding is constant. i.e The energy of the universe, remains constant. But the total energy of the system + the surrounding is constant. i.e The energy of the universe, remains constant. So, the 1 st law of thermodynamics stated that So, the 1 st law of thermodynamics stated that “ energy is conserved” “ energy is conserved” or “ energy can neither created nor destroyed” or “ energy can neither created nor destroyed” BCH 341 lecture 3

Heat and work changes The energy of a system will change if heat is transferred to or from the system or work is done by the system. The energy of a system will change if heat is transferred to or from the system or work is done by the system. 1 st law stated that, if some amount of heat (Q) is added into the system, it must either do work or increase the total energy of the system. 1 st law stated that, if some amount of heat (Q) is added into the system, it must either do work or increase the total energy of the system. BCH 341 lecture 3

In biological system If the capacity to do work is represented by the symbol “W” and “H” stands for enthalpy (or heat content), then the first law can be expressed as: If the capacity to do work is represented by the symbol “W” and “H” stands for enthalpy (or heat content), then the first law can be expressed as: ΔH = Q - W ΔH = Q - W BCH 341 lecture 3

Isothermal nature of cellular process Although heat is the simplest and more familiar medium by which energy may be transferred or used in man-made machines, it is not useful form of energy for performing biological work. Although heat is the simplest and more familiar medium by which energy may be transferred or used in man-made machines, it is not useful form of energy for performing biological work. Why? Why? “ because heat can do work if there is a temperature differential through which it can act” BCH 341 lecture 3

Heat must either pass from one body to another one having lower temperature, Heat must either pass from one body to another one having lower temperature, or the temperature of a given hot body is lowered. Since this is not possible because there are very small temperature differentials in cells which is the basis of doing cellular work……So Since this is not possible because there are very small temperature differentials in cells which is the basis of doing cellular work……So “ living organisms are isothermal” “ living organisms are isothermal” Here we must define another form of energy called Here we must define another form of energy called “free energy” “free energy” BCH 341 lecture 3