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 kJ 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 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? moles of KNO3 How much energy is released or absorbed as the salt dissolves? This quantity is call "q" for the reaction (qreaction). 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= • 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 wate 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=-qsolution- What is the value of qsolution? qsolution= J?
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
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