A little Review on ThermoChem and Gases by David Z Thermochemistry Study of the energy liberated released or absorbed by chemical and physical changes of matter System The part of the universe scientist is interested in Surroundings Everything else in the universe that is outside of the system Closed System A system that does not exchange matter with it s surroundings Open System A system that may change Thermal energy and Matter with its Isolated System A sysem that does not exchange matter or thermal energy surroundings with its surrounding When water freezes is the process Endothermic or Exothermic It s Exothermic because water molecules loses heat to the surroundings Energy The ability to do work Entropy A measure of disorder randomness Closed System Open system Isolated system Heat Capacity C q C T Depends on Substance Depends on mass Specific heat capacity per gram Molar Heat Capacity per mole q m Cs T q n Cm T Example Problem One thing to note that Energy loss energy gained The Iron lost energy because temperature went from 90 degrees to 28 3 degrees That means that the Water the surrounding gained the energy that s why you put a negative sign for water and set the equation equal to each other There is an inverse relationship between heat capacity and temperature change The larger the temperature change the smaller the heat capacity Conversely the smaller the temperature change the larger the heat capacity Calorimetry Process of measuring energy of a chemical reaction by using the heat capacity of the known substance and measuring the temperature change Basically measuring the energy by measuring the temperature change for substances that have a known heat capacity Example Problem Ch 8 Gases Take the shape of their container Highly Compressible Diffuse rapidly Their atoms ions or molecules are randomly distributed Ideal gas law Includes all 3 observations Boyle s Law Charle s Law Avogadro s Law Boyle s Law Pressure and Volume of a gas have inverse relationships Charle s Law When pressure is constant Volume is directly proportional to Temperature V T nR P Avogadro s Law If Temperature and pressure are constant the volume and amount moles are directly proportional for a given mass of ideal gas PV nRT Ideal gas law Example problem Step 1 Write a balanced equation Step 2 Use the Ideal Gas law equation Manipulate the equation to find the number of moles of H2 produced Step 3 Plug in the given numbers into the equation You find the number of H2 produced because 3 90 L of H2 gas is produced Take note that 760 torr 1 atm always convert to atmospheres Temperature is also always in kelvins so convert to kelvins Step 4 So you found the amount of moles produced in the reaction to be 0 154 moles of H2 However in the reaction 2 moles of H2 is produced from every 1 mole of CaH2 That mean you have to divide the 0 154 by 2 to get the of moles of CaH2 Step 5 OK You found the of moles of CaH2 Question is asking of CaH2 in the sample So you have to convert that to grams Step 6 Finally to find the percentage take 3 24 g and divide it by 5 00 g because that was the original sample You yield only 64 7 of CaH2 which is much less because of the impurities in the sample Dalton s Partial Pressure Total pressure Ptotal is the sum of the partial pressures Pxn Ptotal P1 P2 Basically an extension of the Ideal gas law to multiple mixture of gases Partial Pressure Example Step 1 For this problem find the mass of each gas then convert to of moles Step 2 Add up all the moles Then use the ideal gas equation to find the total amount of pressure of gas in the container Step 3 Now multiply the of each pass by the total pressure to find the partial pressures TO BE CONTINUED