Chemistry B- Unit 4: Thermodynamics and Reaction Kinetics

What is true about reaction spontaneity and enthalpy?

Reactions with negative reaction enthalpies are often spontaneous.

Endothermic Exothermic 1 releases heat to the surroundings absorbs heat from the surroundings 2 reactants have higher energy reactants have lower energy 3 the enthalpy of the reaction is positive the enthalpy of the reaction is negative 4 the enthalpy of products is lower the enthalpy of products is higher The table describes exothermic and endothermic reactions. Which row gives correct information?

3

Study the reaction and read the statement. 𝖷𝖾+3𝖥2→𝖷𝖾𝖥6Xe+3F2→XeF6 The rate constant for this reaction is 0.025, and the reaction is second order in Xe and first order in F2. What is the rate of the reaction if [Xe] is 0.25 M, and [F2] is 0.4 M?

6.3 × 10-4

Examine the graph showing energy taken in and released during a chemical reaction over time. Which labeled line represents the activation energy?

A

What happens in an open system?

Both energy and matter can be exchanged freely between the system and its surroundings.

What is calorimetry? Select two that apply.

Calorimetry is the measurement of heat change in chemical and physical processes. Calorimetry measures reactions within an insulated device called a calorimeter.

Study the reaction and the table of four experiments at different concentrations. Which experiment will give the highest reaction rate?

D

After the class learned about heat and temperature, the teacher asked students to brainstorm and make statements about heat and temperature. Here are the responses of the students: John: Energy, like heat, is directly measurable. Emily: Changes in heat can be detected like changes in temperature. Mike: The amount of heat a system loses or gains can be measured. Megan: Heating a substance always increases the temperature of the substance. Which students gave correct information about heat and temperature?

Emily and Mike

Lesson 14

Enthalpy

Lesson 15

Enthalpy Calculations and Entropy

What is true about entropy?

Entropy is the measure of the degree of randomness and disorder in a system.

Which are true about free energy? Select all that apply.

Free energy is a measure of the energy in a system that is available to do work. Free energy indicates whether a reaction will occur spontaneously or not

How is energy conserved in closed systems?

In closed systems, energy can be transferred, usually as heat, between the system and the surroundings. However, energy cannot be created or destroyed in the system.

Why would increasing the temperature of reactants affect the reaction rate? Select two that apply.

Increasing the temperature increases the speed of particles. When particles move faster in the system, they collide more often with each other. Increasing the temperature increases the average kinetic energy of the particles. When the average is higher, any two colliding particles are more likely to have enough energy to react.

Study the chemical reaction. A ⟶ B + C This reaction is second order in A. What is the rate law for this reaction?

Rate = K [A]2

Study the equation. N2O (g) ⟶ N2 (g) + O (g) What is the rate law for this reaction?

Rate = K[N2O]

Study the reaction. NH4+ + NO2- ⟶ N2 + 2H2O The rate of this reaction is proportional to the concentration of ammonium (NH4+) and the concentration of nitrogen dioxide (NO2-). What is the rate law of this reaction?

Rate = K[NH4+][NO2-]

Lesson 17

Rate Laws

Study the reaction and its table of experimental results. 2A + 3B + C →→ D + E What is the rate law for this reaction?

Rate= K[A]2[B][C]

Lesson 16

Reaction Kinetics and Rate

What is true about collision theory?

The particles of the reactants must strike each other with enough energy and the correct orientation.

How do catalysts affect the reaction rate? Select two that apply.

The catalyst changes the orientation of the reactants, which increases the reaction rate. The catalyst provides an alternate pathway with lower activation energy, increasing the reaction rate.

Examine the graph showing energy taken in and released during a chemical reaction over time. What is true according to the information in the graph?

The energy peak shows the activation energy.

Examine the reaction. 𝖢𝖧4 (g)+2𝖢𝖮2(g)→𝖢𝖮2 (g)+2𝖧2𝖮 (g)ΔHcΔS=−890.8 𝗄𝖩=−7.10 𝖩𝖪CH4 (g)+2CO2(g)→CO2 (g)+2H2O (g)ΔHc=−890.8 kJΔS=−7.10 JK What is true according to the reaction?

The enthalpy change in this reaction drives the reaction towards spontaneity. The enthalpy of products is lower than the enthalpy of reactants.

According to collision theory, how do chemical reactions occur?

The particles of the reactants collide with each other with sufficient kinetic energy and correct orientation.

In a reaction between a solid and a liquid, how will breaking the solid reactant into smaller pieces affect the reaction? Select three that apply.

The number of possible collisions will increase. The surface area will increase. The reaction rate will increase.

Study the following reaction: 𝖭𝖧+4(g)+𝖭𝖮−2(g)→𝖭2(g)+2𝖧2𝖮 (l) How does the rate of this reaction change when the temperature is increased?

The rate increases because a higher temperature means that particles move at higher speeds and there are more collisions in the system.

Study the reaction. N2(g) + 3H2(g) → 2NH3(g) How will the reaction rate change when the pressure is increased?

The rate of the reaction will increase.

Study the reaction. 𝖭𝖮 (g)→12𝖭2 (g)+12𝖮2 (g)NO (g)→12N2 (g)+12O2 (g) ∆H = −90.3 kJ What is true about the reaction?

The reaction is an exothermic reaction.

Study the graph. What is true according to the information in the graph?

The reaction is exothermic.

What is Hess's law?

The total enthalpy change in a reaction is the sum of all of the enthalpy changes that occur in the intermediate steps.

Determine if the statement is true or false. A simple calorimeter is an open system while a bomb calorimeter is a closed system.

True

Determine if the statement is true or false. Changing the temperature can affect the reaction rate of a chemical reaction.

True

What is a closed system?

a system that exchanges energy, but not matter, with its surroundings

Study the reactions. 𝖢 (s)+𝖮2 (g)→𝖢𝖮2 (g)ΔH=−393.5 𝗄𝖩C (s)+O2 (g)→CO2 (g)ΔH=−393.5 kJ 𝖧2 (g)+12𝖮2 (g)→𝖧2𝖮 (l)ΔH=−285.8 𝗄𝖩/𝗆𝗈𝗅H2 (g)+12O2 (g)→H2O (l)ΔH=−285.8 kJ/mol 𝖢 (s)+𝖧2 (g)+32𝖮2 (g)→𝖢𝖮2 (g)+𝖧2𝖮 (l)ΔH= ?C (s)+H2 (g)+32O2 (g)→CO2 (g)+H2O (l)ΔH= ? Which steps can be used to calculate the enthalpy of Reaction III correctly?

adding the enthalpy of Reaction I and the enthalpy of Reaction II

Which describes an effective collision?

any collision that results in a reaction

In which type of reaction do the reactants have higher energy than the products, causing heat to be released?

exothermic

What is the energy that transfers from one object to another due to a difference in temperature?

heat

Study the reaction. 𝖭2(g)+3𝖧2(g)→2𝖭𝖧3(g) What change would increase the rate of this reaction?

increasing the pressure of N2

What factor does not affect the reaction rate of a chemical reaction?

molar mass of reactants

What is the enthalpy of combustion?

the enthalpy change that occurs when one mole of a substance completely reacts with oxygen

What is the enthalpy of reaction? Select two that apply.

the enthalpy difference between the products and the reactants the heat transferred between the system and the surroundings during a chemical reaction

What is the enthalpy of formation?

the overall enthalpy change that occurs when one mole of substance is formed from its elements

Examine the given reaction. 𝖭2 (g)+3𝖧2 (g)→2𝖭𝖧3 (g)ΔG=−33.01𝗄𝖩N2 (g)+3H2 (g)→2NH3 (g)ΔG=−33.01kJ What can be deduced from this equation? Select two that apply.

the reaction is spontaneous the entropy of this system has increased

A chemical reaction happens in three steps. Step 1:𝖠→𝖡+𝖢 (𝖿𝖺𝗌𝗍) Step 2:𝖢→𝖣+𝖤 (𝗌𝗅𝗈𝗐) Step 3:𝖣+𝖠→𝖥 (𝖿𝖺𝗌𝗍) What is the rate-determining step?

xxx Steps 1 and 3

According to the second law of thermodynamics, when do natural processes happen spontaneously?

when they increase the entropy of an isolated system

Examine the following reaction. 𝖭2 (g)+3𝖧2 (g)⇋2𝖭𝖧3 (g)ΔH0ΔS0=−92.0 𝗄𝖩=−0.198 𝖩/𝖪N2 (g)+3H2 (g)⇋2NH3 (g)ΔH0=−92.0 kJΔS0=−0.198 J/K What is the correct value for free energy of this reaction at 300 K?

xxx -151.4 kJ

Study the reaction and its table of experimental results. X + 2Y + 3Z →→ 2L + 4T The rate law for this reaction is Rate = K [Y]2[Z] What is the specific rate constant of the reaction?

xxx 1.00

What is true about reaction spontaneity and entropy?

xxx Ice melting in hot water is a nonspontaneous process because it requires a transfer of energy, and ice and water have the same entropy.

Study the reaction and its table of experimental results. 2X + 3Y + Z →→ L + T What is the rate law for this reaction?

xxx Rate= K[X]2[Y][Z]2

Under which circumstances will the reaction rate between a solid and a liquid be highest?

xxx The solid X is in the form of a few smooth spheres. try The solid X is in the form of a single, large cube.

Examine the reaction and the data provided: A reaction is nonspontaneous at low temperatures, spontaneous at higher temperatures, and has a positive ΔS0ΔS0. Which of these must be true at any temperature?

ΔH0 is positive.

Study the reactions. 𝖢 (s)+𝖮2 (g)→𝖢𝖮2 (g)ΔH=−394 𝗄𝖩C (s)+O2 (g)→CO2 (g)ΔH=−394 kJ 𝖧2 (g)+12𝖮2 (g)→𝖧2𝖮 (l)ΔH=−286 𝗄𝖩 H2 (g)+12O2 (g)→H2O (l)ΔH=−286 kJ 𝖢3𝖧8 (g)+5𝖮2 (g)→3𝖢𝖮2 (g)+4𝖧2𝖮 (l)ΔH=−2220 𝗄𝖩C3H8 (g)+5O2 (g)→3CO2 (g)+4H2O (l)ΔH=−2220 kJ 3𝖢 (s)+4𝖧2 (g)→𝖢3𝖧8 (g)ΔH𝖿= ?3C (s)+4H2 (g)→C3H8 (g)ΔHf= ? What is the enthalpy of formation of C3H8(g) in Reaction 4?

−106 kJ

Study the reactions. 𝖢 (s)+𝖮2 (g)→𝖢𝖮2 (g)ΔH=−394 𝗄𝖩 C (s)+O2 (g)→CO2 (g)ΔH=−394 kJ 𝖧2 (g)+12𝖮2 (g)→𝖧2𝖮 (l)ΔH=−286 𝗄𝖩H2 (g)+12O2 (g)→H2O (l)ΔH=−286 kJ 3𝖢 (s)+4𝖧2 (g)→𝖢3𝖧8 (g)ΔH=106 𝗄𝖩3C (s)+4H2 (g)→C3H8 (g)ΔH=106 kJ Target Reaction: 𝖢3𝖧8 (g)+5𝖮2 (g)→3𝖢𝖮2 (g)+4𝖧2𝖮 (l)ΔH= ?C3H8 (g)+5O2 (g)→3CO2 (g)+4H2O (l)ΔH= ? What is the enthalpy change of the target reaction?

−2432 kJ