AP Chemistry Unit 6

The decomposition of A2B is shown by the equation A2B ---> 2A + B. Two possible reaction pathways are shown in the diagram on slide 7. (A) Is this reaction endothermic or exothermic? (B) Describe the direction of heat flow in terms of the system and the surroundings. (C) What is the enthalpy of reaction for the decomposition of A2B in kJ/mol? (D) Why would path 2 require less energy than Path 1? Explain. (E) What is the activation energy of the forward reaction? (F) What is the activation energy of the reverse reaction? (G) What happens to 𝚫H when Path 2 is followed rather than Path 1?

(A) Endothermic (B) Heat is transferred from the surroundings to the system. (C) 120 kJ/mol (D) It has a lower activation energy so each particle would be able to react with less energy. (E) 220 kJ/mol (F) 100 kJ/mol (G) It remains the same

An unknown metal, M, has heated and the heating curve on slide 17 was created. Answer the following with the letter, letter range (ex: A→B) or a temperature. A) Point(s) where only a gas is present B) Temperature at which vaporization occurs C) Point(s) where a mixture of a solid and a liquid are present D) Point(s) where a gas turns into a liquid E) Temperature at which the substance starts to freeze F) Range where there is only a liquid

(A) F (B) 700 degrees C (C) B and C (D) E and D (E) 200 degrees C (F) C to D

An experiment was designed to monitor the flow of heat from a hot piece of metal to water. Shown on slide 8 (a) What is the change in temperature for metal? (b) What time is thermal equilibrium achieved? Justify your answer. (c) Does the average speed of the metal particles increase or decrease with time? Use particle level reasoning to justify your answer.

(a) -62 degrees Celsius (b) 120 seconds. The temperature becomes constant. Prior to the thermal equilibrium the faster molecules are transferring energy to the slower molecules. At thermal equilibrium, all molecules have the same kinetic energy and thus the same temperature. (c) Decrease. The temperature decreases. Temperature is a measure of the average kinetic energy of metal atoms. Since temperature decreases, the average kinetic energy decreases, therefore the average speed of the metal atoms decreases.

A 27.00 g sample of an unknown metal was heated until 4420 J of heat had been added. The graph on slide 13 shows the data collected during the experiment. (a) Determine the temperature change of the metal. (b) Determine the specific heat capacity of the metal. Include units in your answer.

(a) 40 degrees C (b) 0.38 J/g*degrees C

An experiment was performed in an insulated container to determine the energy changes in a chemical reaction. A graph of temperature versus time is shown on slide 3. (a) Is the reaction exothermic or endothermic? Justify your answer using the data provided. (b) A student makes the following statement. Do you agree or disagree? The energy required to break the bonds in the reactants is less than the energy released when the bonds form in the products. (c) Sketch an energy profile diagram for this reaction.

(a) Exothermic. The measured temperature increases. The experiment measures the temperature of the surroundings. Since the temperature of the surroundings increases, heat flow was from system into the surroundings. (b) Agree. Reaction is exothermic so the enthalpy change is negative. The energy required to break bonds (positive) is less than the energy released (negative). Since enthalpy is negative, energy released when bonds formed is greater. (c) See slide 4

Answer the following questions regarding polyethylene terephathalate (PET), the plastic typically used in water bottles. (a) One step is the production of PET involved the crystallization of melted PET. While the plastic is solidifying, is the net flow of thermal energy from the plastic to the surroundings or from the surroundings to the plastic? Justify your answer. (b) Determine the amount of heat, in kJ, involved when solidifying 12.0 moles of PET at its melting point. Heat of fusion = 26.0 kJ/mol. Include the correct sign in your answer.

(a) From the plastic to the surroundings. The formation of a solid involves the formation of attractive forces. Energy is released when attractive forces are formed. the process is exothermic. (b) -312 kJ

(a) The equipment shown on slide 11 is provided so that the student can determine the value of the molar heat of solution for calcium chloride (CaCl2). Knowing that the specific heat of the solution is 4.18 J/(g*degrees C), list the specific measurements that are required to be made during the experiment. (b) Is the dissolving process exothermic or endothermic? Justify using only the data shown on slide 12. (c) Calculate the mass of solution used. (d) Determine the change in termperature. (e) Calculate the moles of CaCl2 dissolved. The molar mass of CaCl2 is 110.98 g/mol. (f) Calculate the molar heat of solution in J/mol

(a) Mass water, mass CaCl2, Initial temperature, final temperature (b) Exothermic: The temperature of the surroundings increased. The process released energy. (c) 50.23 g solution (d) 16.5 degrees C (e) 4.97 g (f) -77300 J/mol

15.0 grams of calcium chloride, CaCl2, is dissolved into 100.0 mL of water at 22.5°C, the final temperature of the solution was 32.2°C. After the dissolution took place, consider the water and what had happened to: a) The temperature? b) The average kinetic energy? c) The average speed? d) Was the dissolution reaction endothermic or exothermic?

(a) increased (b) Increased (c) Increased (d) Exothermic

When 39.0 grams of copper metal at 92.5°C (molar mass = 63.546 g/mol) is dropped into 200. mL of water (molar mass 18.02 g/mol) at 25.0°C, the two substances reach thermal equilibrium. Which substance has: a) Greater kinetic energy? b) Particles with the greatest average speed? c) Highest temperature?

(a) the same (b) water (lighter) (c) the same

Given the heating curve for mercury on slide 16, calculate the heat to freeze 100.0 grams of mercury, Hg, at its melting point.

-1.147 kJ

4NH3(g) + 2O2(g) ---> 2N2(g) + 6H2O(g) If the standard molar heats of formation of ammonia, NH3(g), and gaseous water, H2O(g) are -46 kJ/mol and -242 kJ/mol, respectively, what is the value of 𝚫H°298 for the reaction represented above?

-1270 kJ/mol rxn

Given the following reactions: 2NO (g) + O2 (g) → 2NO2 (g) ΔH = -116 kJ 2N2 (g) + 5O2 (g) + 2H2O (l) → 4HNO3 (aq) ΔH = -256 kJ N2 (g) + O2 (g) → 2NO (g) ΔH = +183 kJ Calculate the enthalpy change for the reaction below: 3NO2 (g) + H2O (l) → 2HNO3 (aq) + NO (g) ΔH = ???

-137 kJ

The reaction for the combustion of methane, CH4, is given below: CH4(g) + 2O2(g) ---> CO2(g) + 2H2O(g) 𝚫H = -802 kJ If 2.38 mol of CH4 reacts with 8.21 moles of O2, how much heat would be evolved?

-1910 kJ of energy released

How much heat is released through the complete combustion of propane, C3H8? C3H8(g) + O2(g) ---> CO2(g) + H2O(g)

-2023 kJ

Is the combustion of propane endothermic or exothermic? How much energy is absorbed or released? Assume standard conditions. C3H8(g) + 5 O2(g) ---> 3CO2(g) + 4H2O(g)

-2043.85 kJ; exothermic

Consider the combustion of methane (CH4). Suppose 39.8 g of CH4 combust according to the following balanced equation. How much heat would be absorbed or produced? What mass of O2 was consumed? CH4(g) + 2O2(g) ---> CO2(g) + 2H2O(l) 𝚫H = -890.1 kj/mol rxn

-2208.6 kj/mol rxn; 128.6 g O2

Aluminum melts/freezes at 933 K. How much energy is required to freeze 2.50 moles of Al at 933 K? ΔHfus, Al= 10.9 kJ/mole ΔHvap,Al= 284 kJ/mole

-27.3 kJ

Spacecraft often use hydrazine, N2H4, as a fuel. How much heat is released during this process for one mole of hydrazine? N2H4 (l) + N2O4 (g) → 2 N2O (g) + 2 H2O (g)

-312 kJ

2H2S(g) + 3O2(g) --> 2H2O(l) + 2SO2(g) 𝚫H° = -1120 kJ/mol rxn If you were to react 7.25 moles of H2S with 9.34 moles of O2, how much heat would be released?

-3490 kJ is the amount that is released, O2 is the limiting reagent

Use the table of standard enthalpies of formation on slide 20, determine the standard enthalpy change of reaction when 2.00 moles of propene combust. The balanced equation for the combustion of 2.00 mol of propene is 2 C3H6(g) + 9CO2(g) ---> 6CO2(g) + 6H2O(g).

-3858 kJ/mol rxn

Calculate the energy released in the reaction between hydrogen and oxygen forming water as shown: H2(g) + O2(g) ---> H2O(g)

-485 kJ

Calculate the enthalpy for the following reaction: 2 A (s) + B (g) → A2B (s) If: A(s) → A (g) ΔH = + 22 kJ 2 A (g) + B (g) → A2B (g) ΔH = - 52 kJ A2B (s)→ A2B (l) ΔH = + 12 kJ A2B (l)→ A2B (g) ΔH = + 32 kJ

-52 kJ

3C2H2(g) ---> C6H6 (g) What is the standard enthalpy change 𝚫H°, for the reaction represented above? 𝚫H°, of C2H2(g) is 230 kJ mol^-1; 𝚫H° of C6H6(g) is 83 kJ mol^-1.

-607 kJ

Given the reaction: AB(g) + 2CD(g) ---> 3EF(g) 𝚫H = -9.52 kJ How many moles of EF would also be produced if the reaction gave off 750 J?

0.236 mol EF

2H2(g) + O2(g) ---> 2H2O(g) 𝚫H° = -481.6 kJ/mol rxn If you performed this reaction and produced 92.1 kJ of energy, how many moles of water were also produced?

0.382 moles H2O

Instant coffee is made through a process called freeze drying. First the coffee is made in the traditional way, and then the coffee is cooled until it becomes a solid, finally the pressure is decreased and the ice changes to a gas, leaving behind the freeze-dried coffee granules. Identify the two phase changes that take place and classify them as endothermic or exothermic.

1. Freezing - Exothermic 2. Sublimation - Endothermic

What three processes take place when a solution forms? Are these endothermic or exothermic?

1. The solvent must expand by overcoming its intermolecular forces. This is an endothermic process. 2. The solute must expand by overcoming its intermolecular forces. This is an endothermic process. 3. The solute and solvent recombine, this process is exothermic.

Use the table on slide 15: Gallium can be purified by melting. How much energy in kJ is required to melt 2 moles of gallium originally at 293 K? Use principles of bonding to explain why the heat of vaporization is much greater than the heat of fusion.

11.7 kJ; Gallium has metallic bonding with metal ions arranged in a lattice with delocalized "sea of electrons" moving freely through the structure. During melting, small separations form within the lattice, allowing the metal to flow. During vaporization, the metal atoms must be completely separated, and this requires far more energy.

What is the reaction enthalpy for the decomposition of baking soda? How much heat is involved when 7.0 g of baking soda is used for your favorite cookie recipe?

135.6 kJ; 5.65 kJ

Calculate the amount of energy needed to boil 91.2 grams of carbon tetrachloride, CCl4, at its boiling point, 350.0 K. ΔHfus= 2.67 kJ/mole ΔHvap= 30.0 kJ/mole Molar Mass, CCl4 = 153.82 g/mol

17.79 kJ

Solid calcium carbonate, CaCO3, is the primary compound in limestone. When it decomposes it forms solid calcium oxide, CaO and gaseous carbon dioxide, CO2. How much heat is absorbed or released during the decomposition of 1.00 mole of calcium carbonate? Assume standard conditions.

179.2 kJ

Hydrazine, N2H4 is formed through the reaction below: 2H2 + N2 ---> N2H4(l) 𝚫H° = +50.63 kJ/mol rxn Calculate the standard enthalpy change when 0.452 moles of N2H4 is formed at 1 atm and 298 K.

22.9 kJ

N2(g) + O2(g) ---> 2NO(g) 𝚫H1 = 180 kJ/mol 2NO2(g) ---> 2NO(g) + O2(g) 𝚫H2 = -112 kJ/mol Given the information above, what is the overall enthalpy change for the reaction given below? N2(g) + 2O2(g) ---> 2NO2(g)

292 kJ/mol

If 26.98 grams of Al and 320 grams of Fe2O3 (molar mass: 160 g/mol) react as completely as possible, how much heat would be released? 2Al(s) + Fe2O3(s) ---> Al2O3(s) + 2Fe(s) 𝚫H = -850.2 kJ/mol rxn

425.1 kJ/mol rxn

1/2H2(g) + 1/2I2(s) ---> HI(g) 𝚫H = 26 kJ/mol rxn 1/2H2(g) + 1/2I2(g) ---> HI(g) 𝚫H = -5.0 kJ/mol rxn Based on the information above, what is the enthalpy change for the sublimation of iodine represented by the equation I2(s) ---> I2(g)?

62 kJ/mol rxn

Nitrogen dioxide, NO2, can be formed from nitrogen and oxygen according to the reaction below: N2 (g) + 2O2 (g) → 2NO2 (g) ΔH = ? Use Hess's Law to calculate the enthalpy for the formation of NO2, using the following two equations: N2(g) + O2(g) → 2NO(g) ΔH= +180 kJ 2NO2(g) → 2NO(g) + O2(g) ΔH= +112 kJ

68 kJ

Calculate the energy involved in the reaction below: CO2 + 2NH3 ---> CO(NH2)2 + H2O

69 kJ

The heat of fusion for water is 6.01 kJ/mole and the heat of vaporization for water is 40.7 kJ/mol, how much energy is needed to melt 22.5 grams of ice?

7.51 kJ

Calculate the enthalpy for the reaction: A + 2B ---> C + 2D If: 4B + 3E ---> 2C 𝚫H = 124 kJ 2D + 3/2E ----> A 𝚫H = -15 kJ

77 kJ

Naphthalene is a primary component of mothballs; they readily sublime at room temperature. The heat of sublimation for naphthalene, C10H8, is 72.9 kJ/mol. How much energy is needed to sublime 15.0 grams of naphthalene? (Molar mass = 128.17 g/mol)

8.53 kJ

Based on the bond energies shown in the table on slide 18, which of the diagrams best represents the change in energy as the reaction represented below proceeds? H2(g) + Cl2(g) ---> 2HCl(g)

A

The enthalpy change for the reaction A ---> x is 𝚫H1. The reaction can be broken down into a series of steps as shown in the diagram on slide 21. Which of the choices on slide 21 shows a relationship that must exist among the various enthalpy changes?

A

Almonds and cashews were burned in a bomb calorimeter containing water. The date on slide 14 was collected. Calculate the heat gained by the water for each nut. Calculate the energy for each nut, which provides more energy per gram?

Almonds: q = 150. kJ; 𝚫H = 25.0 kJ/gram Cashews: 120. kJ; 𝚫H = 24.0 kJ/gram Almonds provide more energy per gram

2H2O2(aq) ---> 2H2O(l) + O2(g) 𝚫H° = -195 kJ/mol rxn The decomposition of H2O2(aq) is represented by the equation above. Assume that the bond enthalpies of the oxygen hydrogen bonds in H2O are not significantly different from those in H2O2. Based on the value of 𝚫H° of the reaction, which of the choices on slide 19 could be the bond enthalpies (in kJ/mol) for the bonds broken and formed in the reaction?

B

The lattice energy for the formation of sodium fluoride, NaF is shown on slide 1. A combination of steps is proposed to be involved in determining the enthalpy of this reaction. Which statement provides the best answer and justification for the energetics of these steps? A. Process 1 is endothermic because energy is released when the attractions between sodium atoms are broken. B. Process 2 is exothermic because sodium has a low electronegativity C. Process 3 is endothermic because energy is required to break the bond D. Process 4 is exothermic because fluorine has a high electronegativity.

C. Process 3 is endothermic because energy is required to break the bond

Which of the following best describes the changes occurring in the reaction represented by the energy profile shown on slide 2? A. 25 kJ is transferred from the system and the products are more stable than the reactants. B. 25 kJ is transferred into the system and the products are more stable than the reactants. C. 25 kJ is transferred from the system and the products are less stable than the reactants. D. 25 kJ is transferred into the system and the products are less stable than the reactants.

D. 25 kJ is transferred into the system and the products are less stable than the reactants.

Methane combusts according to the following equation: CH4 + 2O2 ---> CO2 + 2H2O 𝚫H = -890.7 kJ/mol. At 25 degrees C, very little CO2 or H2O is produced after a few hours when the reactants are mixed. Which of the diagrams on slide 6 could help to explain why the reaction is not producing yield and why?

Diagram 2 because the Ea is so high there would be a lower percent of particles that have enough energy to complete the reaction.

When Urea, H2NCONH2, is dissolved in water a decrease in temperature is measured. A student makes the following conclusion. Do you agree or disagree with the student's conclusion? The decrease in temperature indicates the system is losing heat, suggesting that the dissolving process is exothermic as heat is released when urea hydrogen bonds with water.

Disagree. The decrease in temperature was a measurement of the water which is part of the surroundings. The heat flow was from the surroundings to the system. It is true that urea can hydrogen bond with water and that process is exothermic. However, dissolving also involves breaking attractions among urea molecules and among water molecules. The energy required to break these attractions must be greater than the energy freed when urea hydrogen bonds with water.

Endothermic or Exothermic: Boiling

Endothermic

Endothermic or Exothermic: Changes that involve breaking/separation

Endothermic

Endothermic or Exothermic: Melting

Endothermic

Endothermic or Exothermic: Sublimation

Endothermic

Endothermic or Exothermic: The products are higher in energy than the reactants.

Endothermic

Endothermic or Exothermic: The temperature of the surroundings decreases (your hand feels cold).

Endothermic

Endothermic or Exothermic: Vaporization

Endothermic

When whipped cream is forced out of the can, it is propelled by dinitrogen monoxide gas, N2O. After expelling the whipped cream, the can feels cold. If the can is the surroundings, was the process endothermic or exothermic?

Endothermic

Is the reaction between CH2Cl2(g) + Br2(g) ---> CH2Br2(g) + Cl2(g) endothermic or exothermic? Calculate the energy involved in this reaction.

Endothermic; 55 kJ

Endothermic or Exothermic: Changes that involve combining materials

Exothermic

Endothermic or Exothermic: Condensation

Exothermic

Endothermic or Exothermic: Deposition

Exothermic

Endothermic or Exothermic: Freezing

Exothermic

Endothermic or Exothermic: The products are lower in energy than the reactants.

Exothermic

Endothermic or Exothermic: The temperature of the surroundings increases (your hand feels warm).

Exothermic

Ice melt, calcium chloride, CaCl2, is used in the winter to melt ice on sidewalks and driveways. If the calcium chloride is the system and the ice is the surroundings, was the process endothermic or exothermic?

Exothermic

When water is placed into a freezer, it forms ice cubes. If the water is the system, was the process endothermic or exothermic?

Exothermic

You are stranded and have two plastic jugs, you decide to burn one of the jugs to to send smoke signals and to keep yourself warm, and you decide to save the other jug to carry and store water. One jug is made out of polyvinyl chloride (PVC) and one is made out of polypropylene (PP). Which jug do you choose to burn and why? Combustion of PVC C2H3Cl(g) + O2(g) → CO2(g) + H2O(g) + HCl(g) Combustion of PP C3H6(g) + O2(g) → CO2(g) + H2O(g) ΔHf PVC = 29.6 kJ/mole ΔHf PP = 20.6 kJ/mole

PP because it requires less energy to burn/mol so it will burn at a lower temperature

An experiment was designed to monitor the flow of heat from a hot piece of metal to water. This is shown on slide 9. The red curve represents the average kinetic energy of the water molecules and the green curve represents the average kinetic energy of the metal atoms. Sketch the curve that represents the metal atoms and water molecules at thermal equilibrium.

Slide 10

50.0 grams of Aluminum (specific heat capacity = 0.900 J/g °C) at 85.0 °C was placed into 100.0 grams of water (specific heat capacity = 4.184 J/g °C) at 25.0 °C. The final temperature of the two substances was 30.8 °C. What can be said of the temperature changes for each substance? What is true of the amount of thermal energy exchanged?

The change in temperature of Aluminum is greater than the change in temperature of Water; Same magnitude of thermal energy but opposite in signs.

50.0 grams of Aluminum (specific heat capacity = 0.900 J/g °C) at 85.0 °C was placed into 100.0 grams of water (specific heat capacity = 4.184 J/g °C) at 25.0 °C. What happens to the temperature, average kinetic energy and average speed of the aluminum?

The temperature, average kinetic energy and the average speed of the aluminum atoms decrease as both substances reach thermal equilibrium.

Oranges are typically grown in warm climates because the trees can be damaged by freezing temperatures. If an orange farmer knows that the temperatures are going to drop to below freezing they will spray orange trees with water. Explain why this protects the oranges and orange trees from freezing damage?

The water protects the orange trees by freezing before the oranges do; the process of freezing releases heat which is absorbed by the oranges so they don't freeze.

2.00 g of NaOH is added to 100.0 mL of water at 22.0°C. After dissolving, the temperatures of the solution is found to be 27.3°C. (Assume that the specific heat of the solution is 4.184J/g°C and the density of the solution is 1.00g/mL) a. Find the experimental value for the molar enthalpy of dissolution for NaOH. b. Write the equation for the dissolution of NaOH, including the value for 𝚫H.

a. 2260 kJ b. NaOH(s) + N2O(l) + 2260 kJ ---> NaOH(aq) + H2O(l)

K(s) + 1/2Cl2(g) ---> KCl(s), 𝚫H°f = -437 kJ/mol The elements K and Cl react directly to form the compounds KCl according to the equation above. Refer to the information above and the table on slide 22 to answer the equations that follow. a. Which of the following reactions on the table can be manipulated or combined to form the reaction given above? b. Write an algebraic expression equivalent to 𝚫H° using the variables on the table.

a. 3 b. x/2 + w + y + z + v

A student mixes 0.100 L of 1.00 M HA with 0.200 of 1.00 M MOH according to the reaction below: HA(aq) + MOH(aq) ---> H2O(l) + MA(aq) a. If the temperature of the solutions changed from 22.3°C to 29.1°C, calculate the heat evolved in this reaction. (Assume that the specific heat of the solution is 4.184 J/g°C and the density of the solution is 1.00g/mL) b. Calculate the enthalpy per mole of HA c. If 0.491 mol of HA is reacted with excess MOH, how much heat would be envolved?

a. 8540 kJ absorbed b. 854 kJ c. 4190 kJ

The formation of magnesium oxide, MgO, is shown below: Mg(s) + 1/2O2(g) ---> MgO(s) + 601.7 kJ a. Is this an endothermic or exothermic reaction? b. If 0.321 mol of O2 reacted, how much heat would be absorbed/released?

a. Exothermic b. -386.3 kJ

Ammonia is an important precursor to fertilizer and explosives. It can be synthesized from hydrogen and nitrogen through the Haber-Bosch Process as shown: H2(g) + N2(g) ---> NH3(g) a. Is the reaction endothermic or exothermic and how much energy is involved in the reaction? b. If 15 g of NH3 is synthesized, how much energy is involved in the reaction?

a. Exothermic; -97 kJ b. -42.68 kJ

What is temperature is measure of?

average kinetic energy

Endothermic Process

energy is absorbed by the system from the surroundings

Exothermic Process

energy is released by the system into the surroundings

Surroundings

everything else around the system

Is the formation of dinitrogen tetroxide from nitrogen dioxide endothermic or exothermic? How much energy is absorbed or released? Assume standard conditions.

exothermic; -22.1 kJ

The decomposition of solid iron (III) hydroxide, Fe(OH)3, produces water, H2O, and solid iron (III) oxide, Fe2O3, according to the reaction: 2 Fe(OH)3 (s) → Fe2O3 (s) + 3 H2O (?) If the enthalpy of the reaction is +96.4 kJ/mol Fe2O3, what state is the water? H2O(l) = -285.8 kJ/mol H2O(g) = -241.8 kJ/mol Fe(OH)3(s) = -823.0 kJ/mol Fe2O3(s) = -824.2 kJ/mol

gas

Enthalpy Change of a Reaction

gives the amount of heat energy released (for negative values) or absorbed (for positive values) by a chemical reaction at constant pressure; represented by 𝚫Hrxn; represents the difference in enthalpy between the reactants and products

A solution of ammonium nitrate was created by dissolving 5.02 grams of ammonium nitrate in 100.0 mL of water at 22.3°C. After forming the solution the temperature was 17.3°C. Did heat enter the system or leave the system? What is the sign for q? Was the dissolution process endothermic or exothermic?

heat entered the system; positive; endothermic

Enthalpy

in a constant pressure system, the net energy change; the heat (q) exchanged at constant pressure; represented by 𝚫H

What does the ° symbol mean in 𝚫H°?

indicates that the value is measured in the standard state, which specifies the conditions: For gases: 1 atm of pressure For liquids and solids: the substance's most common stable form at 1 atm and 25°C For solutions: A concentration of 1 M For a compound: 𝚫H° is the enthalpy change when 1 mol of a compound forms from its elements in their standard states For a pure element in its standard state: 𝚫H° = 0 For a pure element not in its standard state: 𝚫H° will not be 0

When bonds are broken, it requires in input/release of energy.

input

In an exothermic process the enthalpy is....

negative

In an endothermic process the enthalpy is....

positive

When bonds are formed, it requires in input/release of energy.

release

First Law of Thermodynamics

states that in an isolated system, heat cannot be lost or gained, it can only be transferred

When we measure temperature changes during a chemical reaction, we are measuring the...

surroundings

Work

the energy needed to move something against a force

Negative bond energy represents...

the energy released when a bond forms.

Positive bond energy represents...

the energy required to break a bond

Molar enthalpy of fusion

the energy required to melt a substance

Molar enthalpy of vaporization

the energy required to vaporize a substance

Calorimetry

the measurement of the quantity of heat exchanged

system

the part of the universe we are studying

universe

the system and the surroundings together

Consider the reaction: 2CIF3 + 2NH3 ---> N2 + 6HF + Cl2. 𝚫H = -1196 kJ/mol. Draw a reaction pathway diagram for this reaction. Label the products, reactants, and 𝚫H.

𝚫H is negative, which is exothermic; the products should be lower than the reactants. Example on slide 5