How Are Temperature and Heat Related? What Are Units for Each?

Thermochemistry Review

How are temperature and heat related? What are units for each?

What is the heat of reaction for NaOH and HCl of 30 mL NaOH and 70 mL HCl go from 21.2 C to 29.5 C?

Compare and contrast Heat of Reaction and Heat of Formation.

Calculate the Heat of Formation – problem #3 page 524.

What is the relationship between heat of reaction and stability of a product?

Draw an energy diagram for a reaction which requires 196 kJ/mol to react and absorbs 124 kJ. Show the other two ways to give the change in energy from the reaction. Is this reaction endothermic or exothermic?

Define enthalpy, entropy, and free energy. What is the relationship between enthalpy, entropy, and free energy?

List three phase changes and tell what is happening to enthalpy and entropy in each.

What is free energy and how is it calculated?

If ΔH is -34 kJ/mol, ΔS is +.98 kJ/mol T, and temp is 189 C, is the reaction spontaneous? Show your work.

What is a reaction mechanism?

Write out a possible reaction mechanism for 2Mg + O2 -> 2 MgO

How are activation energy and activated complex related?

What two things can happen to an activated complex?

What is Hess’s law and what is it used for? Explain the Collision Theory.

Draw energy diagrams for both an exothermic and endothermic reactions. Label E, Ea, Ea’, and where the activated complex would exist.

Name the four factors of reaction rate we can control and explain how/why they impact reaction rate.

Write the heat of formation reaction for the following (use pg 902 for the energies)

NaNO3 Thermochemistry Review Key

How are temperature and heat related? What are units for each? Temperature is a measure of the average kinetic energy in an object. Heat is the transfer of energy due to differences in temperature. Temp = F, C, K. Energy = Joules

What is the heat of reaction for NaOH and HCl of 30 mL NaOH and 70 mL HCl go from 21.2 C to 29.5 C? ΔE = (4.18j/g C)(100 g)(8.3 C) = 3469.4 J /1000 = 3.4694kJ ΔE = -3.4694 kJ The energy the water absorbs is the energy the reaction releases.

Compare and contrast Heat of Reaction and Heat of Formation. Heat of Reaction is the change in energy for any reaction. Heat of Formation is the change in energy in the formation of 1 mole of product at a specific temperature and pressure.

Calculate the Heat of Formation – problem #3 page 524. Find Heat of Formation of S + O2 -> SO2

SO3 -> ½O2 + SO2 +99.1 kJ S + 3/2O2 -> SO3 -395.2 kJ S + O2 -> SO2 -296.1 kJ

What is the relationship between heat of reaction and stability of a product? The more negative the heat of reaction (or formation), the more stable the product(s) will be

Draw an energy diagram for a reaction which requires 196 kJ/mol to react and absorbs 124 kJ. Show the other two ways to give the change in energy from the reaction. Is this reaction endothermic or exothermic?

Ea = 196 kJ ΔH = 124 kJ

A+B -> AB – 124 kJ A + B -> AB ΔH = 124 kJ

Define enthalpy, entropy, and free energy. Ethalpy ΔH – Heat energy in a sample of matter Entropy ΔS – the degree of randomness or chaos in a sample of matter Free energy ΔG – a summation of the possible change due to potential in both Enthalpy and Entropy

What is the relationship between enthalpy, entropy, and free energy? ΔG = ΔH –TΔS, where T is temperature in K. A negative ΔG is a spontaneous reaction

List three phase changes and tell what is happening to enthalpy and entropy in each. Melting both entropy and enthalpy are increasing Evaporating both entropy and enthalpy are increasing Sublimating both entropy and enthalpy are increasing Freezing both entropy and enthalpy are decreasing Condensing both entropy and enthalpy are decreasing Solidifying both entropy and enthalpy are decreasing

What is free energy and how is it calculated? Free energy is a measure of both the entropy and enthalpy of a reaction. It is calculated using the formula ΔG = ΔH –TΔS, where T is temperature in K.

If ΔH is -34 kJ/mol, ΔS is +.98 kJ/mol T, and temp is 189 C, is the reaction spontaneous? Show your work. ΔG = ΔH –TΔS ΔG = (-34 kJ/mol) – (462 k)(.98 kJ/mol K) ΔG = (-34 kJ/mol) – 452.76 kJ/mol ΔG = -486.76kJ/mol

What is a reaction mechanism? The possible method of which bonds of reactants can be broken and bonds of products formed

Write out a possible reaction mechanism for 2Mg + O2 -> 2 MgO

2 Mg + O2 -> 2Mg + 2O 2Mg + O2 ->Mg + MgO2

2Mg + 2O -> 2MgO Mg + MgO2 -> MgO + O + Mg Mg + O -> MgO Mg + Mg + O=O Mg + Mg + O=O Mg + Mg + O + O Mg + Mg-O=O MgO + Mg + O Mg + Mg-O + O MgO + MgO MgO + MgO

How are activation energy and activated complex related? Activation energy is the energy needed to start the reaction, or to bring the reactants together to form an activated complex.

What two things can happen to an activated complex? Form product or break back apart into reactants

What is Hess’s Law and what is it used for? Hess’s law states that It allows us to take reactions that we know the heat of formation or reaction and then combine them to make a reaction we do not know the heat of formation or reaction. If we use the energies from the known reactions, we can calculate the heat of formation/reaction for the new reaction.

Explain the Collision Theory. Reactions happen because reactants collide with enough energy and at the right angle to form new bonds Draw energy diagrams for both an exothermic and endothermic reactions. Label E, Ea, Ea’, and where the activated complex would exist.

Endothermic

Ea ΔH or ΔH’ or ΔE ΔE’

Exothermic

Ea’ ΔH or ΔH’ or ΔE ΔE’

Name the four factors of reaction rate we can control and explain how/why they impact reaction rate. Collision Theory – atoms/molecules must collide with enough energy and the right angle to react.

Heat – more collisions and more energy available Concentration – increases number of collisions Surface area – reactions happen at the surface, so increasing surface area increases the number of atoms/molecules that can react at a given time Catalyst – reduces the activation energy needed to perform a reaction, thereby speeding up the reaction Write the heat of formation reaction for the following (use pg 902 for the energies)

Fe2O3 2Fe + 3/2O2 -> Fe2O3 ΔHf = -824.2 kJ/mol

NaOH Na + 1/2O2 + 1/2H2 -> NaOH ΔHf = -425.9 kJ/mol

CaCO3 Ca + C + 2/2O2 + 1/2H2 -> CaCO3 ΔHf = -1207.6 kJ/mol

NaNO3 Na + 1/2N2 + 3/2O2 -> NaNO3 ΔHf = -467.9 kJ/mol