C7 Flashcards
What is an endothermic reaction?
They transfer energy from the surroundings, causing a fall in temperature.
What is an exothermic reaction?
They transfer energy to the surroundings, causing a rise in temperature.
How would you investigate energy changes?
Get a polystyrene cup, add hydrochloric acid, then add a lid and a thermometer, measuring the temperature increase or decrease that occurs with the addition of a metal.
What are examples of endothermic reactions?
Instant cold packs, photosynthesis
What are examples of exothermic reactions?
Combustion, neutralisation
What is on an exothermic reaction profile?
The reactants start then there is a rise in activation energy and then there is a dip below the reactants line for the products. Overall change is the difference between reactants and products.
What is on an endothermic reaction profile?
The reactants start then there is a rise in activation energy and it dips above the reactants line for the products. The overall energy change is the difference between reactants and products.
What is endothermic and exothermic reactions in the case of bond breaking and bond making?
Energy has to be supplied to break chemical bonds. This means that breaking bonds is endothermic with energy taken from the surroundings. However when new bonds are formed energy is transferred to the surroundings so it is exothermic.
How do you calculate overall energy change?
Add up both sides and subtract the right side from the left and if it is positive it is endothermic and negative it is exothermic.
How can you make a battery?
Add a voltmeter to wires connecting two different metals of different reactivity into a salt solution. The greater the difference in reactivity will mean there is a higher voltage.
What are the formulas for a hydrogen fuel cell?
2H2+O2=2H2O
2H2(g)+4OH-(aq)=4H2O(l)+4e-
O2(g)+2H2O(l)+4e-=4OH-(aq)
Where can hydrogen fuel cells be used?
In cars
What are the pros of a hydrogen fuel cell?
Easy to maintain, no moving parts, water is the only product
What are the cons of a hydrogen fuel cell?
Very expensive, need a constant supply of hydrogen, it is a flammable gas`
