Exothermic and Endothermic Reactions Flashcards
What is a Fuel?
A fuel is a substance that can release stored energy relatively easy
What is a combustion reaction?
A reaction in which a substance reacts with oxygen to produce carbon dioxide CO2 (if completely combusted) or carbon monoxide CO (partially computed possibly due to the lack of 02) and water H2O
What is Enthalpy Change?
A measure of the quantity of energy either absorbed or released during a chemical reaction given the symbol ‘AH’ (the ‘A’ in ‘AH’ is a triangle)
How do you calculate Enthalpy Change?
Enthalpy of the products Hp - enthalpy of the reactants Hr
What is Enthalpy?
Enthalpy is the chemical energy of a substance and is given the symbol ‘H’
How do you know a reaction is exothermic from the enthalpy change?
When Hp is less than Hr, energy is released into the surrounding environment, so the reaction is exothermic. The ‘AH’ will be a negative number ‘-‘.
What is Activation Energy?
For the reaction to occur the bonds in the reactants must break and form new bonds in the products. This is caused by activation energy.
How do you know a reaction is endothermic from the enthalpy change?
When Hp is greater than Hr, energy is absorbed from the surrounding environment, making the reaction endothermic. The ‘AH’ will be a positive number ‘+’.
List the components of an exothermic reaction
- The total chemical energy of the products is less than that of the reactants
- The energy released when the bonds in the products form is greater than the energy required to break the bonds in the reactants
- Excess energy is released into the surroundings
- ‘AH’ is negative
List the components of an endothermic reaction
- The total chemical energy of the products is greater than that of the reactants
- The energy released when the bonds in the products form is less than the energy required to break the bonds in the reactants
- Energy is absorbed from the surroundings
- ‘AH’ is Positive
What happens if the Activation Energy of a reaction is low?
The reaction can occur as soon as the reactants come in contact with one another because they have sufficient energy for a reaction to take place. (may take a longer time)
What are the different units of energy from lowest to highest values?
Describe how to write a Thermochemical Equation
When writing a thermochemical equation you MUST include a fully balanced chemical reaction with states and the enthalpy change at the end of the equation.
Describe the Energy Profile Diagram of an Exothermic Reaction
Describe the Energy Profile Diagram of an Endothermic Reaction
