TEST REVIEW: Thermochemistry (Standards 36-40)

Standards 36 and 37: Understand energy and its forms, including kinetic, potential, chemical and thermal energies. Understand the law of conservation of energy and the process of heat transfer.

Study all of the vocabulary found on the Thermochemistry Notes and Vocabulary Review.

  1. What is the difference between heat capacity and specific heat?
  2. Define: enthalpy of fusion, enthalpy of solidification, enthalpy of vaporization, enthalpy of condensation. Is each one of these processes endothermic or exothermic?
  3. Define standard enthalpy of formation. How is this different from enthalpy of reaction?
  4. What is the difference between potential energy and kinetic energy? How are these terms used in CHEMISTRY?
  5. What is the First Law of Thermodynamics?
  6. Give an example of heat transfer by conduction, convection, and radiation.

Standard 38: Use thermochemical equations to calculate energy changes that occur in chemical reactions and classify reactions as exothermic or endothermic.

  1. Use dimensional analysis to solve for heat in thermochemical equations.

Given the equation:

Si(s) + 2Cl2(g)  SiCl4(l) + 687 kJ

How much heat is produced when 106 g of Cl2 react?

  1. Standard heat of formation. Calculate heat change of a reaction using standard heat of formation or reactants and products. You will be given the relevant valuesof standard enthalpy of formation.

H = Hof(products) – Hof(reactants)

Calculate the change in enthalpy for the following reaction using standard heats of formation. Refer to the Table of Thermodynamic Quantities

Fe2O3(s) + 3CO(g)  2Fe(s) + 3CO2(g)

b. Which reactant is more stable? How do you know?

c. Is this reaction endothermic or exothermic? How do you know?

d. Does the Hrxn indicate that there is more enthalpy in the products or in the reactants in the reaction?

e. Based on enthalpy change alone, would you expect the reaction to be spontaneous at room temperature?

  1. What is the sign of H for an exothermic reaction? Is heat given off or absorbed? Is heat a reactant or a product? If an exothermic reaction was occurring in a flask, what would the outside of the flask feel like? What does the energy graph look like?
  2. What is the sign of H for an endothermic reaction? Is heat given off or absorbed? Is heat a reactant or a product? If an endothermic reaction was occurring in a flask, what would the outside of the flask feel like? What does the energy graph look like?
  3. How does stored chemical potential energy of reactants compare to stored chemical potential energy of products in an endothermic reaction? Exothermic? How does your answer to the previous questions satisfy the law of conservation of energy?
  4. What is the standard heat of formation for any element in its standard state?

Standards 39 and 40: Perform calculations using heat, mass, temperature change, and specific heat. Use calorimetry to calculate the heat of a chemical process.

  1. Convert between different units for measuring heat (joules, kilojoules, calories, kilocalories, and Calories). Conversions can be found on the STAAR chart.

How many kilojoules of energy are in a cookie that contains 150 Calories?

  1. Calculate heat, specific heat, or temperature change using Q = mCpT. You will be given relevant specific heat values.

The temperature of a 6.0 gram sample of glass changed from 20.0 oC to 45.0 oC when it absorbed 550 J of heat. What is the specific heat of this glass sample?

  1. What is the final temperature when a 15.0 g bar of nickel at 100.0 ºC is dropped into 55.0 g of water at 23.0 ºC? Use cp = 4.186 J/g·ºC for water. Use cp = 0.440 J/g·ºC for nickel. (Show all of your work! Round final temperature to tenths place. Don’t forget units!)
  1. Calculate heat change using the change in water as your reference point in calorimetry.

Q = mCpT

Two water solutions that have a density of 1.00 g/mL are mixed, and a chemical reaction occurs. The temperature rises from 25.0 oC to 27.0 oC. Given that the specific heat capacity of water is 4.18 J/(g x oC) and that the total mass of the mixture is 75.0 g, what is the heat change for the reaction?