4.5.1 Exothermic and endothermic reactions Flashcards
4.5 Energy Changes (14 cards)
What can be classified as the system?
The reactant (reacting) particles
What can be classified as the surroundings?
- Air
- Solvent
- Equipment
- Everything Else (The rest of the Universe)
- You
What is endothermic energy?
Energy absorbed from surroundings
What is exothermic energy?
Energy released to the surroundings
How can we represent these reactions?
Using energy profile diagrams
What factors make a reaction endothermic?
- If arrow from an energy profile diagram goes up
- There is energy put in to break bonds
- Energy is absorbed from the surroundings
- Thermometer decreases
What factors make a reaction exothermic?
- If arrow from an energy profile diagram goes down
- There is energy released to surroundings when bonds are formed
- Surroundings get hotter
- Thermometer increases
What is activation energy and where would it be drawn on the energy profile diagram?
The minimum amount of energy required to start/activate a reaction.
It would be drawn vertically from the reactant line to the top of the curve.
Compare how an exothermic and endothermic energy profile diagram look.
EXOTHERMIC:
- The reactant line would be above the product line.
- Change in heat line would go vertically from the start of the curve to the product line.
- The curve would go up from reactants to the activation energy level then back down to the product line.
ENDOTHERMIC:
- The reactant line would be below the product line.
- Change in heat line would go vertically from the reactant line to the end of the curve.
- The curve would go up from reactants to the activation energy level then back down to the product line
If you saw an exothermic graph and were asked why this reaction is exothermic, you would say the following. But first, fill in the gaps:
This reaction is __________ overall because the _________ released when bonds are __________ is __________ than the energy required to __________ bonds in the __________.
This reaction is exothermic overall because the energy released when bonds are formed is greater than the energy required to break bonds in the reactants.
If you saw an exothermic graph and were asked why this reaction is exothermic, you would say the following. But first, fill in the gaps:
This reaction is __________ overall because the _________ required to __________ bonds in the reactants is __________ than the energy __________ when bonds are __________ in the __________.
This reaction is endothermic overall because the energy required to break bonds in the reactants is greater than the energy released when bonds are formed in the products.
What is the equation for calculating energy released?
Q = m * c * ^T
(^ means change)
How do you calculate overall energy change?
OEC = Energy required to break bonds in reactants - Energy required to break the bonds formed in the products
What does the overall energy change show if it is negative?
That the reaction is exothermic. (So therefore if the OEC is positive the reaction is endothermic)
