Thermochemistry Quiz

Solutions Below Thermochemistry Quiz Topic List: Endothermic and Exothermic reactions. Endothermic: the system absorbs (gains) energy (q). The surroundings lose energy. Exothermic: the system loses (gives away) energy (q). The surroundings gain energy. Energy diagrams: If the energy of the products is larger than the energy of the reactants, it is endothermic. If the energy of the products is less than the energy of the reactants, it is exothermic. Specific heat (C): the energy required to raise 1 gram of a substance by I degree Celsius. Calculate q: q = m*Delta*TC m: mass of the sample. Delta*T : change in temperature. Delta*T = Tfinal-Tinitial. Specific heat of a metal: You have the mass of both the metal and water. You will have different initial temperatures of the metal and the water. The final temperature of the metal and the water is the same. You know the specific heat of water. Solve for q of water. Q for the metal is the same number but the opposite sign (+/-), Solve for C of the metal. Heating curves: Phase change and temperature change together. Generally of water. Within a particular state of matter, use q = m*Delta*TC Remember that the specific heat is different for different for different states of matter. There is no temperature change during phase change. You will be given the mass of a sample. Delta*H is in kJ/mol. Convert the mass to moles. Then, use Delta*H to convert from moles to kJ. Convert from kJ to J by multiplying by 1,000. Add up all of the stages that you went through (up to 5). Answer in joules (J). Heat of Solution: A mass of a compound is dissolved in water. The water (with a given mass) changes temperature, Calculate q for the water. Q for the compound is the same number. Calculate the energy released/absorbed if 1 mole of a compound dissolves: Start with 1 mole of the substance as a given. Convert to grams of the substance that is dissolved. Finally, use the energy (q) that you solved for over the grams (mass) that created that energy. Answer in kJ (divide by 1,000). Test-Thermochemistry Name Select the letter of the best answer for the questions below: 4. The physical properties of gases, liquids, and solids are a result of a. the strength of attractive forces c. molar masses and densities X b2 a. original temperature of the substance d. b. the heat capacity d. the melting and boiling point temperatures 2. The amount of temperature increase in a substance being heated depends primarily on the c. size and precision of the calorimeter 3. The specific heat of a pure substance b. specific heat and mass of the substance d. quantity of heat added to the substance a. is the same for each of the states (solid, liquid, gas) of the substance b. varies in proportion to the temperature change of the substance c. depends whether the substance is being warmed or cooled d. expresses the rate of temperature change when energy is added or removed 4. Which of the following terms represent opposite changes of state? X a. heat of fusion and melting c. evaporation and vaporization C 5. In order to melt ice, d a. crystals must be formed c. heat must be added from the surroundings 6. A plateau on a heating curve indicates that a. only one phase is present c. all of the heat has been removed from the substance b. condensation and freezing d. sublimation and deposition b. the surrounding temperature must be above 5 deg * C d. heat must be removed by the surroundings b. the substance has stopped absorbing/releasing energy d. a phase change is occurring Use the following enthalpy profile to answer questions #7-12. The reaction could be described as: A + B -> AB 40 1 mole Delta plus/minus 1 mole of B enthalpy, kJ 30 20 10 1 mole/AB 0 reaction progress 7. What is the value of the enthalpy of the reactants? a + 30 kJ b.-30 kJ b 8. What is the value of AH for the reaction to form AB? b.-30 kl d + 40kJ a 9. If the heat term were placed in the balanced chemical equation for the reaction shown above, the heat term would be written a. on the product side, with a + sign c. on the product side, with a sign b. on the reactant side, with a sign d. on the reactant side, with a + sign 10. What would be Delta*H for the reverse reaction, in which substance AB reacts to form b-30 kJ c.-10 kJ D 11. How are the two reactions and related? a. the first reaction is endothermic second exothermic (AB -> A + B) * I (A + B -> AB) b. the first reaction is exothermic and the second one is endothernic c. both reactions are exothermic d. both reactions are endothermic d. A +B7 c + 40kJ c.+ 10kJ a + 30kJ a + 30 d - 40kJ Delta*H