Please answer these two questions : 1.* How would you explain to a friend (who i
ID: 1024926 • Letter: P
Question
Please answer these two questions:
1.* How would you explain to a friend (who is not a scientist) why one salt causes the waterto get cold, while the other causes the water to get hot or a third may not change the temperature very much at all?
2.
EXPERIMENT 8 Energy Changes in Chemical Reactions INTRODUCTION The energy changes that take place in chemical reactions are used for a wide variety of applications in our daily lives, including, life. We burn fuels to heat our homes and propel our cars and planes. We burn calories, in the form of carbohydrates, fats and proteins, in our bodies to stay alive. (A calorie is defined as the amount of heat needed to raise the temperature of 1 gram of water by 1C; nutritionists use the term Calorie (capital C) to represent a kilocalorie or 1000 calories). These are just some simple examples of chemical reactions that we use daily for our energy needs. The chemical reactions mentioned above can be represented by the following chemical equations: Combustion of Octane CH18 O2CO2HOEnergy 1303 kcal/mole Respiration in the Body CO2 + O + Energy (670 kcalm ole) In the case of combustion of octane in an automobile or other vehicle, the energy produced is in the form of heat (also known as enthalpy) and motion (kinetic energy). This is obvious from the heat given off by a car engine when it is running and the motion comes about when the combustion causes the gases in the cylinder of a car to expand and forces the pistons to move, which in turn propels the car when it is in gear. We can see that the explosion in the combustion process is what provides the force in the cylinder that pushes the piston. The car engine is a relatively simple system compared to the body. In the body we have not only heat and motion generated, but there are numerous other energy consuming processes taking place, such as movement of chemicals (ions and molecules) across membranes in the cells of our bodies, nerve signals being transmitted through our bodies and so on. The body must 29Explanation / Answer
1) Some salt dissolves in water and its particles get homogeneously distributed in the solution breaking apart from each other with the release of energy.This released energy causes the water to get hot.
Some other salts are more stable in solid form so need energy is needed for its particles to break apart and get homogeneously distributed in the solution.So, these salts absorbs energy from water and then its particles break apart with the expense of the absorbed energy.This absorbed energy from water causes the water to get cold.
2)The salt with negative heat of solution releases heat to the solvent,in which it is mixed.So these salts can melt ice to water by raising its temperature and itself gets dissolved in the melted ice(water)
examples-NH4NO3 Q=-6.2kcal/mol
NaCl Q=-1.2kcal/mol