ENDOTHERMIC & EXOTHERMIC PROCESS

Endothermic and Exothermic Processes

Exothermic- the word describes a process that releases energy in the form of heat.

Forming a chemical bond  releases energy and therefore is an exothermic process.

Exothermic reactions usually feel hot because it is giving heat to you.

Endothermic - a process or reaction that absorbs energy in the form of heat.

Breaking a chemical bond requires energy and therefore is Endothermic.

Endothermic reactions usually feel cold because it is taking heat away from you.

Exothermic Processes	Endothermic Processes
freezing water solidifying solid salts condensing water vapor making a hydrate from an anhydrous salt forming an anion from an atom in the gas phase Annihilation of matter E=mc2 splitting of an atom	melting ice cubes melting solid salts evaporating liquid water making an anhydrous salt from a hydrate forming a cation from an atom in the gas phase splitting a gas molecule separating ion pairs cooking an egg baking bread

Endothermic and exothermic reactions involve the absorption and release, respectively, of energy to and from the environment.

Exothermic Reaction

An Exothermic Reaction releases energy upon completion.

KEY POINTS

• All chemical reactions involve the transfer of energy.
• Endothermic processes require an input of energy and are signified by a positive change in enthalpy.
• Exothermic processes release energy upon completion, and are signified by a negative change in enthalpy.

TERMS

• endothermic
  of a chemical reaction that absorbs heat energy from its surroundings
• exothermic
  of a chemical reaction that releases energy in the form of heat
• enthalpy
  In thermodynamics, a measure of the heat content of a chemical or physical system.

EXAMPLES

• An example of an exothermic reaction is the mixing of water and strong acids. In the presence of water, the acid will dissociate quickly and release heat.
• An example of an endothermic reaction is the melting of an ice cube. In order to melt the ice cube, heat is required.

1. 

   fig. 2

   Endothermic Reaction

   An endothermic reaction requires energy for completion because the energy of the reactants is less than that of the products.

2. Endothermic and Exothermic Reactions

    An energy diagram can be used to show energy movements in these reactions and temperature can be used to measure them macroscopically.

REVIEW


Many chemical reactions release energy in the form of heat, light, or sound. 
These are exothermic reactions. 

• Exothermic reactions may occur spontaneously and result in higher randomness or entropy (ΔS > 0) of the system. They are denoted by a negative heat flow (heat is lost to the surroundings) and decrease in enthalpy -  the amount of heat content used or released in a system at constant pressure. 
• In the lab, exothermic reactions produce heat or may even be explosive. 

• There are other chemical reactions that must absorb energy in order to proceed. These are endothermic reactions. 
• Endothermic reactions cannot occur spontaneously. Work must be done in order to get these reactions to occur. When endothermic reactions absorb energy, a temperature drop is measured during the reaction. 

Endothermic reactions are characterized by positive heat flow (into the reaction) and an increase in enthalpy (+ΔH). 

Examples of Endothermic and Exothermic Processes

• Photosynthesis is an example of an endothermic chemical reaction. In this process, plants use the energy from the sun to convert carbon dioxide and water into glucose and oxygen. 

•  An example of an exothermic reaction is the mixture of sodium and chlorine to yield table salt. 

ENDOTHERMIC & EXOTHERMIC QUIZ - turn into drawer