Energy Calculations Flashcards
What is the amount of energy released by by fuels measured in
Joules or sometimes calories
What is the conversion rate between calories and joules
1 cal: 4.2 J
What is used to measure the amount of energy released when substances burn
Calorimeter
What type of reaction occurs when fuels and foods react with oxygen
Exothermic
What is the simplest calorimeter and how does it work
Some water in atlas beaker of metal can, when the substance burns it heats the water and the rise in temperature depends on the amount of energy released
What is the equation you use to calculate the amount of energy transferred
Q=mcΔT
Q is the amount of energy transferred in joules
M is the mass of water in grams
C is the specific heat capacity in water in J/gdegrees
ΔT is the temperature change in degrees
Why do simple calorimeters not give accurate results
Because much of it was used to heat the surroundings
How can the results of simple calorimeters be used
To compare the energy released by different fuels
What can be used to compare the energy released by burning different fuels
The energy change in kj per gram or the energy change in kj per mole can be used
How can the energy change in kj/mol can be calculated
By multiplying the energy change in kj/g by the relative formula mass
What happens when a reaction takes place in a solution
Energy is transferred to or from the solution
How can you reduce the energy transferred into the surroundings of reactions in solutions
In an insulated container
When calculating the temperature change of a solution what do we assume?
They behave like water;
1 cm3 of the solution has a mass of 1g
The specific heat capacity of water is 4.2J/gdegrees
What do we assume when we add a solid to water or a solution in order to calculate the energy transferred
We assume that the volume of the volume doesn’t change and that 1cm3 has the mass of 1g and that its specific heat capacity is 4.2
What can we use to show the energy changes for chemical reactions
Energy level
What does the difference between the energy levels of reactants and products represent
The energy change for the reaction
What must happen in order for a reaction to happen
During a chemical reaction bonds in the reactants must be broken for the reaction to take place
What causes energy to be taken in an endothermic reaction
Breaking bonds
What is the minimum energy required for a reaction to take place called
Activation energy
Why are a reactions endothermic
When new bonds are formed in the products which release energy
What is energy needed for in a reaction
To break the bonds
What is released when new bonds are formed in products
Energy is released
What makes the overall reaction exothermic or endothermic
The difference in these energy changes
What is the bond energy
The energy needed to break the bond between 2 atoms
How can we use the bond energies to calculate the overall energy change
An equal amount of energy is released when the bond forms between 2 atoms and so we can use bond energies to calculate the overall energy change for a reaction
What are bond energies measured in
KJ/mol
What steps are required to calculate the energy change for a reaction
The total amount of energy needed to break all of the bonds in the reactants
The total amount of energy released in making all of the bonds in the products
The difference between the two totals
Why are fossil fuels bad
They are non renewable and cause pollution
What are the advantages of using hydrogen as a fuel
It burns easily and releases a large amount of energy per gram
It produces no carbon dioxide when it is burned, only watwer
Where can hydrogen be used
In combustion engines
In fuel cells to power vehicles
What is the disadvantage of using hydrogen as a fuel
It is flammable and not safe
Supply and storage issues
What do vehicles that use fuel cells need to match normal cars on
Performance, convenience, cost
