6. Chemical Energetics Flashcards
What do the terms exothermic and endothermic mean
Endothermic - a reaction that takes in heat energy from the surroundings
Exothermic - a reaction that give out energy to the surroundings
Give an example of a type of reaction that is exothermic
Combustion
Neutralization
Give an example of an endothermic reaction
Thermal decomposition
Photosynthesis
In terms of bond energies what happens during a chemical reaction
Energy is needed to break bonds and is released when bonds are made
Exothermic - energy released from making bonds is greater than the energy used to break bonds
Endothermic - energy required to break bond is greater than the energy released when making bonds
Mexo
Bendo
What is a reaction profile
A graph which shows the relative energies of reactants and products as well as the activation energy of the reaction
Draw a reaction profile for an endothermic reaction
Draw a reaction profile for an exothermic reaction
Label the following reaction profiles as exothermic or endothermic
How can the energy change of a reaction be calculated from bond energies
Energy change (kJ molˆ-1) = total energy of bonds broken - total energy of bonds made
If the energy change of a reaction is negative, is the reaction exothermic or endothermic
Exothermic
Energy has been lost to the surroundings
Fill in the gap
Fuels are burned to resales ___ ___
Heat energy
Which colourless gas can be used as a fuel
Hydrogen
What is a fuel cell
A cell that continually produces a voltage as long as it is supplied with oxygen and a fuel
What is the only product of a hydrogen-oxygen fuel cell
Water
Write an equation for the overall reaction that takes place in a hydrogen-oxygen fuel cell
2H2 + O2 —> 2H2O
What are the advantages of fuel cells
No pollution produced
Produce more energy than an alternative fuel like petroleum
Continuous process as long as fuel is supplied
What are the disadvantages of fuel cells
Materials used to make them are expensive
High pressure tanks required to store oxygen and fuels like hydrogen
Hydrogen is expensive and hard to store
Temperature affects efficiency
