a) A chemistry student finds a shiny rock that she suspects is gold. She determines that its mass is 14.3 g. She then fi

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A A Chemistry Student Finds A Shiny Rock That She Suspects Is Gold She Determines That Its Mass Is 14 3 G She Then Fi 1 (187.33 KiB) Viewed 21 times

a) A chemistry student finds a shiny rock that she suspects is gold. She determines that its mass is 14.3 g. She then finds that the temperature of the rock rises from 25°C to 52°C upon absorption of 49.4 J of heat. Find the heat capacity of the rock and determine whether the value is consistent with the heat capacity of gold (The heat capacity of gold = 0.128 J/g °C). b) A 55g piece of metal is heated to 99.8C and then plunged into a beaker of water. The beaker holds 225g of water and its temperature is 21°C before the metal contacts it. The final equilibrium temperature of the system is 23.1°C. Could it be possible that the metal in question is iron? (The specific heat capacity of water is CH2O = 4.184 J g'K' and that of iron is Ciron = 0.469 J/gK). c) A piece of zinc weighing 35.8 g was heated from 20.00°C to 28.00°C. How much heat was required? The specific heat of zinc is 0.388 J/(g°C). d) Calculate the total heat energy that is needed to convert 200 g of water 25 °C to steam at 120 °C. The heat of vaporization of water is 2256 J/g; the heat capacity of water is 4.184 J/g and the heat capacity of steam is 1.86 J/g. e) A 328 g sample of water absorbs 5.78 x 10 J of heat. Calculate the change in temperature for the water. If the water is initially at 25.0°C, what is its final temperature? Take the specific heat capacity of water to be 4.184) g 10c-1. f) Calculate the total heat energy that is needed to convert 200 g of ice at -25 °C to steam at 150 °C. The heat of fusion of water is 333 J/g; the heat of vaporization of water is 2256 J/g; the heat capacity of ice is 2.06 J/g; the heat capacity of water is 4.184 J/g and the heat capacity of steam is 1.86 J/g. Enthalpy a) consider the equation N2(g) + O2(g) → 2NO(g) Given the following data, calculate the standard enthalpy of formation of NO(g). (5) N2(g) + 2O2(g) 5 2NO2(g) AH = 66.6 kJ mol! 2NO(g) + O2(g) 5 2NO2(g) AH =-114.1 kJ mol! b) Use Hess's Law to calculate the enthalpy change for the formation of CS2 (1) from C (s) and S(s) (5) C(s) +2 S(s) → CS2 (1) from the following enthalpy values. C(s) + O2(g) → CO2 (g) AH1 = -393.5 kg S(s) + O2(g) → SO2 (g) AH2 = -296.8 kJ CS2 (1) + 3 O2 (g) → CO2 (g) + 2 SO2 (g) AH3 = -1103.9 kJ c) Write the equation whose enthalpy change represents the standard enthalpy of formation of NO(g). Y2N2(g) + 1202(g) → NO(g) Given the following data, calculate the standard enthalpy of formation of NO(g). N2(g) + 2O2(g) 5 2NO2(g) AH° = 66,6 kJ mol-' 2NO(g) + O2(g) 5 2NO2(g) AH° =-114.1 kJ mol-' d) Methyl alcohol, CH3OH, is toxic because liver enzymes oxidize it to formaldehyde, HCHO, which can coagulate protein. Calculate AH° for the following reaction: (5) 2CH3OH(aq) + O2(g) → 2HCHO(aq) + 2H2O(1) Take into consideration the following standard enthalpies of formation: CH3OH(aq): -245.9 kJ/mol HCHO(aq): -150.2 kJ/mol H2O(1): -285.8 kJ/mol