Week 12 Ch 14: Thermodynamics Flashcards
Spontaneous processes
Both chemical reactions and physical change occur in one particular direction only under particular conditions of temperature and pressure. The system moves to a more stable state via the reactions and changes. Such a process is said to be spontaneous.
A spontaneous process that once started proceeds without the involvement of any outside factors. E.g. Na metal in water, Ice melting, Iron rusting
A spontaneous process favours the formation of products
Non-spontaneous process
The system moves to a more stable state via the reactions and changes. If the system moves from more stable state to less stable state via reaction and changes, the process is non-spontaneous.
In contrast with a spontaneous process, a non-spontaneous process requires an involvement of outside factors. E.g. electrolysis of water, reduction of iron oxide
a non-spontaneous process does not favour the formation of products
A spontaneous process that once started proceeds without the involvement of any outside factors. E.g. Na metal in water, Ice melting, Iron rusting
Calorimetry
The heat transfer associated with changes of its state due to chemical reactions, physical changes or phase transitions can be measured by calorimetry using a calorimeter.
The transferred heat is measured by changes in a body of known properties such as temperature volume, length or phase change.
Types of systems
Open system: mass and energy can be gained or lost across their boundaries.
Closed system: energy, but not mass, can be gained or lost across their boundaries.
Isolated system: mass or energy cannot be exchanged with surroundings.
Thermodynamic functions
Internal energy (U): the sum of energies for all of the individual particles in a sample matter. It simply refers to the energy contained within a thermodynamic system or thermal energy.
Enthalpy (H): a function related to the heat adsorbed or evolved by a chemical system. Is is also defined as the sum of the system’s internal energy and the product of its pressure and volume.
Entropy (S): a measure of the number of way energy is distributed throughout a chemical system. It is also related to a state of disorder, randomness or uncertainty.
Gibbs free energy (G): a energy that is available to do work. It can be referred to a thermodynamic potential which is also used to calculate the maximum work.
State vs. path
State functions are “variables” that define the state of a system. When you have a system you need to be able to define the conditions in which it exists before and after a change. We typically referred to these as the initial and final states. By states, we mean the system can be described by a set of properties.
A state function depends only on the initial and final states of the system. Therefore, the route dose not matter
Air travel routes from Brisbane to Christchurch may be more than one (Orange vs. blue route).
The initial state is Brisbane and the final state is Christchurch regardless of the route taken. Both initial and final latitude and longitude are also state function.
Time taken and distance travelled depends on its route. Hence, they are not state functions.
calorimetry definition (video on slide)
Calorimetry is the process of measuring the amount of heat released or absorbed during a chemical reaction. By knowing the change in heat, it can be determined whether or not a reaction is exothermic (releases heat) or endothermic (absorbs heat).
2 types of properties of matter
P______
C______
Physical properties:
Observed and measured without changing chemical identity of sample
Chemical properties:
observed and measured as sample changes to chemical identity
what are extensive and intensive properties and variables of chemicals (has video)
Extensive properties and variables depend on the amount of material. These are a material’s properties such as mass and volume.
Intensive properties and variables are independent of the amount of material. These are either properties like temperature or others that combine, or are the ratio of, two extensive variables like density (mass/volume) or molar concentration (mole/volume).
Law of thermodynamics
The first law of thermodynamics is the law of conservation of energy. It states that the total energy of an isolated system is constant. Energy only can be transformed from one form to another but can be neither created nor destroyed.
Exothermic and endothermic
Exothermic:
- thermal energy transfer from system to surroundings
- Negative sign as the system lost energy
Endothermic:
- thermal energy transfer from surroundings to system
- Positive sign as the system gained energy
Enthalpy definition
Enthalpy is a thermodynamic property and a state function, defined as the sum of the internal energy and the product of pressure and volume in a system at a constant pressure. The internal energy and pressure-volume work requires a tedious process to find out the changes in volume, enthalpy is a much more convenient to use.
Hess Law (Has video)
Hess’ law states if a reaction is conducted in a series of steps, ΔH for the overall reaction will equal the sum of the enthalpy changes for the individual steps.
Entropy definition (has video)
Entropy (S) is a measure of energy dispersal, as a function of temperature, during a process. It represents the unavailability of a system’s thermal energy for conversion into mechanical work. Spontaneous reactions proceed in the direction that leads to lower energy or higher entropy. Therefore, entropy predicts processes’ reversibility.
Second law of thermodynamics (has video)
Entropy predicts the direction of spontaneous processes and determines whether they are irreversible or reversible. The second law of thermodynamics states that the entropy of the universe increases for spontaneous processes.
