Which of the following reactions is exothermic?
1. Na(s) --> Na(g)
2. Na(g) --> Na+ + e-
3. Cl2(g) --> 2Cl(g)
4. Cl(g) + e- --> Cl-1
My guess is 4, but I'm not sure
Here is what you do.
For 1, do we think it will take energy to change Na as a solid to Na as a gas. If you don't know much about Na, think about ice(that's a solid). Do you think it takes energy to melt the ice from a solid to a liquid, raise the temperature to boiling, then boil all the water to steam. Of course it takes energy to do that. If we must add energy it is endothermic. So Na(s) ==> Na(g) is an endothermic reaction and you don't check that one. Use that same kind of reasoning for 2,3, and 4.
For 2 you are removing an electron. For 3 you are separating two Cl atoms. In 4 you are adding an electron to an almost filled shell.
Thanks DrBob
exothermic reaction is one that releases heat. Adding an electron to a chlorine atom releases energy.
Cl(g) + e- Cl-(g)
Thanks Randy
, that is correct. The correct answer is 4, Cl(g) + e- --> Cl-1.
Based on your analysis and the information provided, you are correct. Reaction 4 (Cl(g) + e- --> Cl-) is the exothermic reaction among the options given.
The correct answer is indeed 4. The reaction Cl(g) + e- --> Cl-1 is an exothermic reaction because it releases energy. When an electron is added to a chlorine atom, it fills up the valence shell, resulting in the formation of a chloride ion (Cl-1). This process releases energy in the form of heat.
To determine whether a reaction is exothermic or endothermic, you can consider the overall change in energy during the reaction. If the reaction releases energy (typically in the form of heat), it is exothermic. If the reaction absorbs energy from the surroundings, it is endothermic.
In this case, you can use your knowledge of the nature of the reactions to make an educated guess. Reaction 1 involves the conversion of Na(s) to Na(g), which requires adding energy to break the metallic bonds holding the sodium atoms together. Therefore, it is an endothermic reaction. Reaction 2 involves the removal of an electron from a sodium atom, which releases energy, making it an exothermic reaction. Reaction 3 involves the separation of chlorine molecules into individual chlorine atoms, and this process also requires energy input, so it is endothermic. Finally, in reaction 4, an electron is added to a chlorine atom, releasing energy and making it an exothermic reaction.
By analyzing the nature of the reactions and understanding the concepts of energy changes in chemical reactions, you can identify that reaction 4 is the exothermic one.