U-world: Gen-Chem: Thermo chemistry#2

Which of the following reaction coordinate diagrams best represents the two-step reaction involving tyrosine to nitrotyrosine in a lipid environment?

**Based on the passage, the nitration of tyrosine in a lipid environment is a two-step reaction. The first step has a ΔG of −91.8 kJ/mol with a large activation energy, and the second step has a ΔG of −14.1 kJ/mol with a smaller activation energy.

Which of the following are true concerning the overall reaction in an aqueous environment?

-The rate constant increases exponentially with increasing temperature. -The rate constant increases exponentially with decreasing activation energy. -The reaction rate decreases exponentially with increasing activation energy.

Characteristic of ideal gas

-There are no attractive or repulsive forces between the gas molecules. -The size (molecular volume) of the individual gas molecules is negligible. -Collisions between the gas molecules are completely elastic. -Ideal gas molecules have an average kinetic energy (energy of motion) that is directly proportional to the gas temperature.

In the Pourbaix diagram

-show the relationship between chemical species as a function of given conditions. -Straight line= equilibrium unaffected by pH!

The bond enthalpy ΔH°298 (bond dissociation energy)

-the energy needed to homolytically break 1 mole of a given type of bond between two atoms in the gas phase at a temperature of 298 K -ΔH∘rxn=∑(ΔH∘298 broken bonds)−∑(ΔH∘298 formed bonds)

Which of the following pressure measurements is equivalent to a pressure of 152 mmHg?

0.2 atm and 20.3 kPa **1 atm=760 mmHg=760 torr=101,325 Pa=101.325 kPa

Consider the dimerization of nitrogen dioxide at room temperature: 2 NO2(g)⇌ N2O4(g) Keq = 8 atm-1 If the equilibrium partial pressure of nitrogen dioxide in a container is 0.5 atm, what is the partial pressure of dinitrogen tetroxide?

2 atm

The equilibrium HC2H3O2+H2O ⇄ H3O++C2H3O^−2 exists in a 1 M aqueous solution of HC2H3O2 with an equilibrium constant Keq = [H3O+][C2H3O2−]/[HC2H3O2]. Which of the following expressions explains why Keq does not include a term for [H2O]?

[H2O] ≈ 55.5 ≈ constant **As the solvent, water cannot have a concentration of zero.

If the first step of the nitration of tyrosine in a lipid environment is slower than the second step, what is the rate law for the overall reaction?

Rate = k1[tyrosine][O3]

Reaction quotient

Ratio of the concentrations of the products to the concentrations of the reactants at any point during the reaction aside from equilibrium, where each reactant and product in the expression is raised to the power of its stoichiometric coefficient. Commonly denoted by Q.

Irreversible reactions tend to be under kinetic control, which favors products whose pathways have the lowest activation energy.

Reversible reactions tend to be under thermodynamic control, which favors the most stable product.

Pressure

force/area

Equilibrium is reached in a reversible reaction when the rate of the forward reaction equals the rate of the reverse reaction. The graph shows the changes in concentration during the formation of HI(g) from a mixture of H2(g) and I2(g). If the measurement is taken at equilibrium, how many moles of HI(g) are present in a 750 mL sample of the reaction mixture?

4.5 mol

Assume that helium behaves as an ideal gas. What is the estimated density of 1.0 g of helium gas at a temperature of 27 °C and a pressure of 3.0 atm? (Note: Use R = 0.0821 L∙atm∙mol−1∙K−1)

4.9 × 10−4 g/mL

When ammonia burns in air, nitrogen dioxide and water are produced according to the reaction below: 4 NH3(g) + 7 O2(g) → 4 NO2(g) + 6 H2O(l) At 0 °C and 1 atm pressure, burning 44.8 L of ammonia requires:

7/2 moles O2 **Under conditions of standard temperature and pressure (STP), which is defined as 0 °C and 1 atm of pressure, a gas occupies a volume of 22.4 L for every 1 mole of gas molecules.

Liquid nitrogen is used in cryosurgery for wart removal (N2 liquefies at −196 °C and freezes at −210 °C). Which temperature range coincides with the condensation of N2 gas?

75-79 K

inelastic collision

A collision in which the colliding objects become distorted, generate heat, and possibly stick together.

The diagram below shows the activity of cerium oxides that have been proposed as catalytic materials to reduce emissions of nitrogen monoxide, carbon monoxide, soot, and hydrocarbons during the combustion of diesel fuel. Based on the diagram, if the reactions are irreversible, which of the following does NOT illustrate a function of the cerium oxide catalyst?

CO2 + Ce2O3 → 2 CeO2 + CO **The diagram of the cerium oxide catalyst shows that CO is converted into CO2; therefore, if the reactions are irreversible, the catalyst would NOT function for the reverse reaction (converting CO2 to CO)

PV=nRT

Ideal Gas Law

Which gas would occupy more volume at a constant temperature and pressure, 1.5 g of N2 gas or 1.5 g of O2 gas?

N2 because there are more moles of N2

Keq and heat

The equilibrium constant Keq is defined as the ratio of the reactants and products when a reaction is in equilibrium, and only changes in temperature can alter Keq.

Given that entropy is negative (disorder decreases) in the reaction, which of the following statements is true regarding the formation of aqueous nitrotyrosine?

The overall reaction becomes less thermodynamically favorable at higher temperatures. **ΔG = ΔH − TΔS

Because step 2 of the reaction in aqueous phase is rate-limiting, the formation of ROI from tyrosine and ozone in step 1 can be assumed to reach a state of equilibrium. Tyrosine(aq)+ O3(aq)⇌ ROI(aq) + HO3(aq) Which of the following will occur if the temperature of this system is raised from 298.15 K to 350 K?

The reaction will be driven toward the reactants.

Equilibrium

achieved in a reversible reaction when the forward reaction and the reverse reaction occur simultaneously at the same rate.

The reversible reaction Hb+4O2⇄Hb(O2)4 exists in blood between hemoglobin (Hb) and oxyhemoglobin Hb(O2)4. According to the law of mass action, doubling the O2 concentration would:

decrease the reaction quotient by a factor of 1/16.

The Arrhenius equation

describes the relationship between the rate constant and the temperature and activation energy of a reaction.