THIS QUESTION MUST BE COMPLETED Solid potassium nitrate dissolves in water according to the equation below. KNO3 (s)-K* (aq) + NO3(aq) AH* = +34.89 kJ 15.00 grams of solid KNO3 dissolves in 125.0 grams of water initially at a temperature of 25.00 °C in a perfect calorimeter. Calculate the final temperature of the solution in the calorimeter. [You may assume that no heat escapes the calorimeter and that all solutions have the same specific heat capacity as pure water (4.184 J/g °C)] • Is this salt dissolving process Endothermic or Exothermic? Endothermic • Does the chemical reactions (salt dissolving) release or absorb energy? Absorb AH for the reaction above is +34.89 k) per mol of KNO3 that dissolves. This is the quantity that tells us how much energy is released or absorbed as the salt dissolves. It is usually measured in kj per mol. However, we are not dissolving 1 mol of salt in this experiment, we are dissolving 15.00 grams of KNO3. How many moles of KNO3 are being dissolved? 101.1 moles of KNO3 How much energy is released or absorbed as the salt dissolves? This quantity is call "q" for the reaction (reaction). It is a measure of the amount of heat released or absorbed by the chemical reaction based on the amount used in this particular experiment. Greaction 5177.68 • Energy does not escape the calorimeter. We must account for all of that energy. If energy is released by the reaction (the salt), it must go somewhere. Where does it go? It goes INTO the water in the calorimeter. If the reaction absorbs energy, where does it get it? It gets it by pulling it out of the water. Notice how the direction (sign) of the energy transfer changes depending on which point of view we take, the salt or the water. When we measure the temperature in the calorimeter we are measuring the temperature of the WATER (solution). Therefore there is a difference in sign for the energy transfer. Greaction-solution What is the value of solution? solution -5177.68 J? • How do we relate energy (g) to temperature change (AT)? They are related though a property called the Specific Heat Capacity of the substance. Specific Heat Capacity is given the symbol "Cp" or sometimes just "S.H.". q=mass-C₂ AT or q=mass-S.H.AT So, we can relate the temperature change for the solution to "q" for the chemical reaction taking place in the solution. solution = mass-Cp.AT and Greaction-solution These two can be combined in order to relate the heat change for the reaction to the measured temperature change for the solution greaction=-mass-Cp-ATsolution . With a "perfect" calorimeter, we assume that the calorimeter itself absorbs no heat and does not allow any energy to escape. Thus, all of the energy is transferred to or from the contents of the calorimeter. What is the "total mass of the contents of the calorimeter grams If we want to calculate the temperature change AT for the contents of the calorimeter, we need to know the specific heat capacity of the solution in the calorimeter. If the solution is sufficiently dilute (not much salt compared to water) then the specific heat capacity of the water with the salt dissolved in it (the solution) will be very close to that of pure water. For water Cp = 4.184 g C AT= • What is the final temperature of the solution in the calorimeter? Tfinal- °C