Thermodynamics Flashcards

What is thermodynamics?

Principles that govern energy transformations in chemical reactions.

What are the potential energies?

• Heat (Temperature)

• Kinetic (Motion)

• Chemical (Chemical Bonds)

What makes an energy potential?

The ability to be transferred or do work

What is a system?

All reactants, products, the solvent containing them, and the immediate atmosphere.

What is the universe?

System and its surroundings

What is an isolated system?

A system that exchanges neither matter nor energy with its surroundings.

What is a closed system?

A system that exchanges energy but not matter with its surroundings.

What is an open system?

A system that exchanges both energy and matter with its surroundings.

The energy of a molecule depends on what 3 factors?

• Covalent bonds

• Non-covalent interactions

• Level of freedom in its structure

What is energy in a system?

A state function

Heat is represented by what letter and unit?

Q and calorie

Heat and work use calorie as their unit. What does this unit represent?

The amount of heat it takes to raise the temperature of one gram of water by one degree Celsius at sea level.

Enthalpy (H) refers to what?

The heat content of the reacting system dependent on the number and kinds of chemical bonds.

Define exothermic

Negative delta H. When a chemical reaction releases heat.

Define endothermic

Positive delta H. When reacting systems take up heat from the surroundings.

How is delta H calculated?

H (products) - H (reactants) … under constant pressure.

Explain the term bond energy and its relationship to bond formation / breaking.

The energy exchanged between the system and its surrounding when a chemical bond is formed or broken.

Bond formation causes energy release

Bond breaking requires an energy input

Do free atoms have more or less energy compared to those engaged in a bond or interactions?

More

What is the first law of thermodynamics?

Energy can be transferred and transformed but it cannot be created or destroyed. The energy of the universe is constant.

Energy thats “unusable” between the transfer from system to surroundings leads to an increase in what?

“Randomness” of the universe. Entropy.

What is Entropy?

A form of energy (S) that increases with temperature. A state of more disorder; i.e. a state of less potential energy. Increase in entropy is often a spontaneous process.

What is the 2nd Law of Thermodynamics?

In any chemical or physical process, the entropy of the universe always increases, making the universe more disordered

What intra-molecular factor affect entropy?

• Temperature conformations like…

• Translational

• Vibrational

• Rotational

What intermolecular factor affect entropy?

• State of matter

• Non-covalent interactions

• Molar concentration

• Concentration gradient

Does entropy increases predict spontaneous reactions?

No, not always. (Water freezing to ice or condensation of water vapors)

What determine if a reaction will process spontaneously?

Free Energy. Delta G.

What is the Gibbs equation?

G=H-TS

What are exergonic reactions?

Reactions that proceed with a net loss of total potential energy (free energy). Delta G < 0. Spontaneous. Energy released to the environment.

What are endergonic reactions?

Energy-requiring reactions, which proceed with a net gains of total potential energy (free energy). Delta G > 0. Non-spontaneous. Energy is absorbed from the environment.

At equilibrium what remains the same even if the concentration of products or reactants changes?

The reactant to product ratio

What conditions are you in for standard free energy change? Delta G degree.

• 1 molar starting concentration of each of the reactants and products

• Temperature at 25 degrees Celsius (298 K)

• 1.0 atm (atmospheric pressure)

• Reaction allowed to proceed to completion or an equilibrium

What conditions are you in for biochemical standard free energy change? Delta G degree comma.

• Same conditions at standard free energy change plus…

• pH = 7.0

• Concentration of water is omitted (even if participatory in rxn)

When a reacting system has a free energy change of zero what can be said about that system?

There is no potential energy. The system is in equilibrium.

Define spontaneous

A process that proceeds forward in the direction in which it is written. A → B.

Living cells always maintain a state of what?

Chemical disequilibrium

How is Keq calculated?

[Products] / [Reactants] … once at equilibrium

What are characteristic of each reaction?

Keq and standard free energy change

How are delta G degree comma and Keq related?

Delta G degree comma = -RT ln Keq

In exergonic reactions is there more products or reactants at equilibrium?

Products

In endergonic reactions is there more products or reactants at equilibrium?

Reactants

What is relationship between delta G comma and “non-standard” concentrations of reactants and products?

Delta G comma = Delta G degree comma + RTln ([C][D]/[A][B]) … Note: first term is at equilibrium, second term is from at that point in the rxn.