topic 5-energy changes

Created by

Aswini+ Krishnathasan+

Cards (31)

energy profile for exothermic reactions
A) activation energy
B) products
C) reactants
D) energy change from reactants to products
energy profile for endothermic reaction
A) products
B) activation energy
C) reactants
D) energy change from reactants to products
Exothermic reaction 
Reaction where energy is released to the surroundings, usually in the form of heat
Endothermic reaction 
Reaction where energy is absorbed from the surroundings
Activation energy
Minimum energy required for reactant particles to collide and react
Higher activation energy 
More energy required to start the reaction
Lower activation energy 
Less energy required to start the reaction
Activation energy is shown on reaction profiles as the difference in energy between the reactants and the highest point on the curve
Examples of exothermic reactions 
Combustion reactions
Neutralization reactions between acids and bases
Most oxidation reactions
Energy can't be created or destroyed, it can only be transferred from one place to another
Examples of endothermic reactions
some sports equipment
thermal decomposition
Bond energy 
The amount of energy needed to break one mole of a particular covalent bond
bond breaking is endothermic as energy must be supplied to break existing bonds
bond formation is exothermic as energy is released when new bonds are formed
in exothermic reactions the energy released by forming bonds is greater than the energy used to break them
in endothermic reactions the energy used to break bonds is greater than the energy released by forming them
the overall change= energy of reactants- energy of products
What type of reaction produces a negative energy change?
exothermic
Cells contain chemicals which react to produce electricity.
The voltage produced by a cell is dependent upon a number of factors including the type of electrode and electrolyte.
A simple cell can be made by connecting two different metals in contact with an electrolyte.
Batteries consist of two or more cells connected together in series to provide a greater voltage.
In non-rechargeable cells and batteries the chemical reactions stop when one of the reactants has been used up. Alkaline batteries are non-rechargeable.
Rechargeable cells and batteries can be recharged when an external electrical current is supplied because the chemical reactions are reversible.
the bigger the difference in reactivity of the electrodes, the bigger the voltage of the cell
when two metals(electrodes) are dipped in a salt solution(electrolyte) and joined by a wire the more reactive metal will donate electrons to the less reactive metal
Fuel cell 
A type of electrochemical cell which converts energy between electrical and chemical forms
Hydrogen-oxygen fuel cell
Combines hydrogen and oxygen to form water while generating electrical energy
how hydrogen-oxygen fuel cells work
Hydrogen is oxidized at the anode, releasing electrons.
The electrons flow through a wire to the cathode.
Hydrogen ions travel through the electrolyte to the cathode.
Oxygen, hydrogen ions, and electrons combine to form water.
A) hydrogen enters
B) negative anode
C) positive cathode
D) oxygen enters
E) electrolyte
F) water out
G) wires
advantages of hydrogen fuel cells
do not need to be electrically charged
no pollutants are produced
can be a range of sizes for different uses
disadvantages of hydrogen fuel cells
hydrogen is highly flammable
hydrogen is difficult to store as it is a gas
hydrogen is sometimes produced for the cell by non-renewable sources