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# 2011 hr thermo study guide key

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### 2011 hr thermo study guide key

1. 1. 2011 Honors Thermochemistry Study Guide Key1. The study of heat changes that accompany chemical reactions and phase changes is_thermochemistry_______________.2. _Heat_________ (q) – Energy that is in the process of flowing from a warmer objectto a cooler object. Heat is measured by _temperature________________.3. _Endothermic____________ Reactions are chemical reactions that must absorb energyin order to occur. The ∆ H rxn charge is always positive_____________.4. _Enthalpy__________– (H) -the heat content of a system at constant pressure.5.____Potential___________ energy is the stored energy an object has based on itsposition or composition.6. _Combustion____________________ The enthalpy change for the complete burningof 1 mole of the substance.7. The Law of ___Conservation of Energy______________________ states that in anychemical reaction or physical process, __energy_________ can be converted from 1 formto another, but it is neither created nor destroyed.8. _Kinetic_____________ energy is energy of motion9. __Specific Heat__________________ is the amount of heat required to raise thetemperature of 1 g of a substance by 1° C10. _Energy__________- the capacity to do work or to transfer heat.11. _calorie___________________ is the amount of heat required to raise thetemperature of 1 g water by 1° C12. __Exothermic_____________ reactions are chemical reactions that release energy.The ∆ H rxn charge is always __negative_______________. Energy Conversions 1 Calorie = _1_____ kilocalorie = ____1000___ calories 1 calorie = ___4.184_______ joules 1 kilojoule = __1000______ joules 1. Convert 42.3 Calories to kilojoule176.98 2. Convert 0.050 kilocalories to joules209.2 3. Convert 13.8 joules to Calories0.0033 4. Convert 27 kilojoules to calories6453.15 5. Convert 23.3 Calories to joules97487.2 6. Convert 380 kilojoules to kilocalories90.82
2. 2. Specific Heat 1. It took 137.2 J of heat to raise the temperature of 15.7 g of a substance by 52 º C. What is the specific heat of the substance?0.16 2. When 32.4 g of zinc absorbs 105 J of heat energy, what is the change in temperature of the metal?8.31 3. Determine the amount of heat released if 11.5 g of lead melted with a change in temperature of 34.3 º C.63.112 4. A sample of magnesium cooled from 90.6 º C to 37.6 º C and produced 2329 joules of energy. What was the mass of the sample?43.08 Calorimetry 1. A sample of silver with a mass of 40.1 g is heated to a temperature of 95.6 °C and placed in a container of water at 23.5 °C. The final temperature of the silver and water is 76.5 °C. What mass of water was in the container?0.82 2. A 250 g sample of an unknown solid is heated to 87 °C and placed into a calorimeter containing 25.6 g of water at 32.4 °C . If the final temperature of the solid sample and the water is 54.6 °C , what is the specific heat of the solid?0.29 3. A 67 g sample of iron metal is heated and put into 10.5 g of water at 98.7 °C in a calorimeter. If the final temperature of the iron sample and the water is 122.8 °C, what was the temperature of the iron sample when it was placed in the water?158.39 4. A sample of aluminum with a mass of 42 g is heated to a temperature of 62.5 °C and placed in a container of water at 26 °C. The final temperature of the aluminum and water is 59.8 °C. What mass of water was in the container?0.72
3. 3. Enthalpy Identify the type of reaction and whether it is endothermic or exothermic: 1. CaCO3 (l)  CaO (g) + CO2 (g) vaporization endothermic 2. NH3 (g)  NH3 (l) condensation exothermic 3. S (l) + O2 (l)  SO2 (s) solidification exothermic 4. NH4NO3 (s)  NH4 (l) + NO3 (l) fusion endothermic 5. CH4 + O2  CO2 + H2O combustion exothermic 6. How much energy is released by burning 75.6 grams of ethanol? 2242.88 7. How much energy is released by melting 42.3 grams of methanol? 4.26 8. How much energy is absorbed by 1.7 moles of water becoming steam? 69.19 9. How much energy is released by 88.2 grams of water condensing to a liquid?199.43 10. How much energy is absorbed by 7.3 grams of liquid ammonia becoming a solid?2.43 11. Calculate the total energy required to pass through each phase in order to melt 75.5 grams of ice from – 36.5 oC to 146 oC. Show each calculation and the total amount.239.9 Hess’ Law and Heat of Formation 1) Given that the heat of formation of calcium carbonate is –1207 kJ/mol, the heat of formation of carbon dioxide is –394 kJ/mol, and the heat of formation of calcium oxide is –635 kJ/mol, determine the heat of reaction. CaCO3  CO2 + CaO 178 2) Given that the heat of formation of methane is –75 kJ/mol and the heat of formation of carbon tetrachloride is –135 kJ/mol, determine the heat of reaction. CH4 + 2 Cl2  CCl4 + 2 H2 -60 3) Given that the heat of formation of potassium chloride is –436 kJ/mol and the heat of formation of potassium chlorate is –391 kJ/mol, determine the heat of reaction. 2 KCl + 3 O2  2KClO3 90 4) Calculate the heat of reaction for the formation of barium sulfate and water. BaO + H2SO4  BaSO4 + H2O ∆H = ? a) BaO + SO3  BaSO4 ∆H = -213 kj
4. 4. b) SO3 + H2O  H2SO4 ∆H = -78 kj-1355) Calculate the heat of reaction for the formation of Tin (IV) chloride. Sn + 2 Cl2  SnCl4 ∆H = ? a) Sn + Cl2  SnCl2 ∆H = -325 kj b) SnCl2 + Cl2  SnCl4 ∆H = -186 kj-511 Entropy1. ___entropy_____________ (S) – a measure of the disorder or randomness of theparticles that make up a system2. _spontaneous_reaction_______________ – a change that occurs with no outsideintervention.3. Law of _Disorder/entropy____________– Spontaneous processes always proceed in away that the entropy of the universe _increases____________.Describe the movement and order of molecules in the following phases:4. Solids –no movement, low entropy5. Liquids – little movement, some entropy6. Gas – lot of movement, high entropy7. Entropy __decreases__________ as a substance changes from gasliquidsolid.Does entropy INCREASE or DECREASE with the following phase changes:8. As methanol (l) solidifies (s) _decrease_______________9. As ice (s) turns to vapor (g) _increase_______________10. As water (g) condenses (l) _decrease_______________11. As water (l) vaporizes (g) _increase______________12. As a metal (s) melts to liquid (l) _increase_______________13. As methanol (g) turns to methanol (s) _decrease_______________