Thermochemistry and Kinetics - AP Chemistry

The entropy cannot decrease in an isolated system because the energy can only be degraded. Since the system is isolated, no higher-grade energy—or any energy at all—is being introduced into the system. As a result, the entropy cannot decrease. The other answer choices relate to the other laws of thermodynamics.

Standard states are defined as a specific set of conditions, such as when a gas is at , concentration, and .

Standard enthalpy of formation, the energy required for form 1 mole of a compound from its constituent elements, occurs when elements are in their standard states.

is positive because heat flows into the system to raise the temperature of the water.

Use the equation that relates heat, mass, specific heat, and change in temperature:

There are four main laws of thermodynamics, which describe how temperature, energy, and entropy behave under various circumstances. The zeroth law of thermodynamics helps to define temperature; it states that if two systems are each in thermal equilibrium with a third system, they must be in thermal equilibrium with each other. The first law of thermodynamics negates the possibility of perpetual motion; it states that when energy passes into or out of a system, the system's internal energy changes in accord with the law of conservation of energy. The second law of thermodynamics also negates the possibility of perpetual motion; it states that in a natural thermodynamic process, the sum of the entropies of the interacting systems increases. Lastly, the third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature nears absolute zero.

According to Le Chatelier's principle, an increase in the concentration of reactants will cause the reaction to shift to the right in order to re-establish equilibrium. Thus, immediately after reactant A is added, the forward reaction will increase and the net rate of formation of the products will be positive.

The integrated rate law shown is for a reaction rate law with a first-order dependence on reactact A. If such a rate law accurately describes the kinetics of the reaction, then ln\[A\] will vary linearly with respect to time.

Since reactant molecules collide and interact to break old bond and form new ones, any factors affecting collision and interactions will affect the reaction rate. Thus, increasing temperature will increase both the frequency of collisions and the average kinetic energy of the molecules. Enzymes bring molecules close to each other and orient them in a way that facilitates reactions.

If the activation energy of the forward reaction is greater than that of the reverse reaction, the products must have a higher enthalpy than the reactants. The net enthalpy change is therefore positive, meaning that it is endothermic.

If the activation energy of a forward reaction is greater than that of the reverse reaction, thenthe products must have a higher enthalpy than the reactants (draw a potential energy diagram to visualize).

The rate-determining step in a reaction mechanism is a kinetic bottleneck, in that it prevents the overall reaction from proceeding; thus, it is what determines how quickly the overall reaction can proceed.

Eocell = Eo cathode - Eoanode

Eocell = 0.80 – (-0.76) = 1.56 V

Eocell = Eo cathode - Eoanode

Eocell = 2.87 – (1.50) = 1.37 V

Activation energy is the energy barrier that needs to be overcome for a reaction to proceed; the higher the activation energy, the slower the reaction. Activation energy can only be altered via a catalyst. Catalysts are chemical substances that lower the activation energy, allowing reactions to proceed faster. Other physical quantities such as temperature and pressure don’t alter the activation energy.

Reaction rate is a direct measure of the speed of a reaction. As mentioned, increasing activation energy will increase the barrier and, therefore, slow down the reaction.

Catalysts are chemical substances that decrease the activation energy, thereby increasing the reaction rate. They are commonly used in chemical reactions to drastically speed up reactions that might otherwise take hours or days to complete. Enzymes are biological catalysts that facilitate most of the biological reactions happening in our bodies.

This question is asking about the relationship between activation energy of a reaction (kinetics) and the amount of products produced (equilibrium). Remember that altering the speed of a reaction (kinetics) does not change the equilibrium of the reaction. Increasing or decreasing activation energy (which alters the speed of reaction) will simply allow for the reaction to proceed slower or faster, respectively. It will not change the amount of products produced at the end.

Activation energy is the difference between the energy of the transition state and the energy of the reactant. Recall that activation energy is the energy barrier that needs to be overcome by a reaction. The transition state is a higher-energy, intermediary molecule that lies in between the reactants and products. It is created when reactants are in the process of becoming products. Therefore, to get to products, it is necessary to go through this high-energy transition state.

Activation energy is the energy needed to climb this energy “hill” (energy needed to go from reactants to transition state); therefore, the activation energy is the energy of the transition state (top of the energy hill/barrier) minus the energy of the reactant.

Catalysts are substances that increase reaction rates without being consumed in the reaction. They decrease the activation energy needed, and they do not always need to be in the same phase as the reactants. In heterogeneous catalysis, the catalyst is in a different phase than the reactants. Equilibrium concentrations of both reactants and products are unchanged by the addition of a catalyst.

All of the choices are true, except that catalysts can be in distinct phases than the reactants. These are known as heterogenous catalysts.