Chapter 16- Thermodynamics

Define: Spontaneous Process

A process that proceeds on its own without any external influence or input of energy

Define a state function.

A state function is a function or property whose value depends only on the present state (condition) of the system, not on the path to arrive at that condition.

True or False: The standard enthalpy of formation of a pure element is always negative.

False: Standard enthalpy of formation for a pure element is always zero.

True or False: Standard entropies of reaction cannot be calculated without knowing the enthalpy of reaction.

False: Standard entropies of reaction can be calculated from standard entropies of formation

True or False: A spontaneous process occurs without any external energy and occurs quickly.

False: though a reaction does occur without any external energy, a spontaneous reaction is not necessarily a quick reaction; it could proceed very slowly.

True or False: ∆H determines whether a reaction is spontaneous or nonspontaneous

False: ∆G determines the spontaneity of a reaction.

When Q is less than K, what direction does the reaction proceed?

Forward direction.

What phase changes occur when ∆S is negative and ∆H is negative?

Gas to liquid, liquid to solid, and gas to solid.

What is the second law of thermodynamics?

In any spontaneous process, the goal entropy of a system and its surrounding always increases.

Define reaction quotient Q

Is defined in the same way as the equilibrium constant K [Kc =(C)*c(D)*d÷(A)*a(B)*b] except that the concentrations or partial pressures in the equilibrium constant expression are not necessarily equilibrium values.

Define Standard free-energy change (∆G°)

Is the change in free energy when reactants in their standard states are converted to products in their standard state.

Define Standard free energy of Fromation (∆G°f)

Is the the free-energy change for the formation of 1 mol of the substance in its standard state from the most table form of its constituent elements in their standard states.

What is a standard state?

Mosyt stable form is at 25°C and 1 atm, and 1 M for solutions

Do spontaneous processes move towards or opposite of equilibrium?

Moves towards

What are the five state functions we most commonly use and/or consider?

Pressure, volume, temperature, enthalpy, and entropy.

When Q is greater then K, what direction does the reaction proceed?

Reverse direction.

What phase changes occur when ∆S is positive and ∆H is positive?

Solid to gas, liquid to gas, and liquid to solid.

Like equilibrium, spontaneity is depended on what three components?

Temperature, pressure, and the composition of the reaction mixture.

Define the molar heat capacity.

The amount of heat needed to raise the temperature of 1 mol of a substance by 1°C.

Define Free energy. What denotes free energy? State its equation.

The capacity of a system to continue a chemical reaction. It is denoted by G. G= H-TS

Define Activation energy (Ea)

The energy difference between the transition state and the reactants, is the minimum collision energy needed for reaction.

Define standard molar Entropy (S°).

The entropy of 1 mol of the pure substance at 1 atm pressure and a specified temperature, usually 25°C.

What is the third law of thermodynamics?

The entropy of a perfectly ordered crystalline substance at zero K is zero.

What is thermodynamics?

The study of energy changes in chemical reactions

What is the first law of thermodynamics

The total energy of a system and its surroundings is constant in any process.

True or False: A reaction that is spontaneous and endothermic will have a large positive ∆S.

True

True or False: A spontaneous reaction always increases the total entropy of the system plus the surroundings.

True

True or False: An increase in temperature always leads to an increase in entropy.

True

True or False: The standard molar entropy of a pure substance is always positive

True

True or False: The temperature of a reaction system determines the relative importance of the enthalpy and entropy terms.

True

True or False: If ∆H is negative and ∆S is also negative, the reaction will be spontaneous at low temperatures.

True: A lower temperature will reduce the contribution of the entropy term, allowing the enthalpy to dominate.

Define Stadard entropy of reaction (∆S°)

∆S°=S°(products) - S° (reactants) ∆S°= [c S°(C)+ d S° (D)] - [a S°(A) + b S° (B)]