Energy changes Flashcards
What is an exothermic reaction
A reaction that transfers energy from the reacting molecules to the surroundings
What happens to the surroundings if an exothermic reaction occurs
The temperature would increase
Is combustion an exo or endo reaction
Exo
How could we represent the energy changes that take place in reactions
Using an energy profile diagram
Two uses of exothermic reactions
Hand warmers
Self-heating cans e.g. for food or drink
What is an endothermic reaction
Endothermic reactions take in energy from their surroundings
What happens to the surroundings if an endothermic reaction occurs
The temperature of the surroundings decreases
What is an e.g of endo reaction
Thermal decomposition
What tells us the energy that has been released to the surroundings in an energy diagram
The difference between the energy of the reactants and the energy of the products
Activation energy
The minimum energy required for a reaction to occur
Where is the activation energy on a energy profile diagram
The activation energy is from the reactants to the peak of the curve
Are exothermic reactions energy changes shown as negative or positive and why
Negative, because energy has been transferred from the chemicals.
In endothermic reactions, energy is gained from the surroundings.
Endothermic energy changes are shown as positive, because energy has been gained.
Fuel cells electrode equations
At the negative electrode: 2H2 + 4OH- → 4H2O + 4e-
At the positive electrode: O2 + 2H2O + 4e- → 4OH-
