Energy calculations Flashcards
Why don’t simple calorimeters give accurate results for the energy released?
much of its used to heat surroundings
What is calorimetry used for?
measuring amount of energy released when substances burn e.g by heating water in a glass or metal container.
Can be used to compare amount of energy released by fuels and food
How do you calculate energy change in KJ/mol?
Energy change in KJ/g
x
Relative formula mass
What happens when a reaction takes place in a solution?
energy is transferred to or from the solution.
What does a insulated container do to reactions?
reduced energy transfers to surroundings
What does assuming a solution behaves like water mean for the mass and specific heat capacity?
1cm3 of solution has a mass of 1g and specific heat capacity of 4.2J/g^c
When do we assume happens when solid added to water of aqueous solution?
no change in volume
What is the equation to calculate amount of energy transferred?
Q=mcDT
Q= energy transferred (J) m= mass (g) c= specific heat capacity (J/g^c) DT= temperature change (^c)
What do energy level diagrams show?
relative energies of reactants and products
Activation energy
Overall energy change of reaction
What is energy required?
Breaking bonds
when is energy released?
Making new bonds
What is activation energy?
the minimum amount of energy required for a reaction to happen
What is an exothermic reaction?
more energy released forming new bonds in the products than the amount of energy required to break bonds in the reactants
What does a catalyst do?
provides alternative pathway with lower activation energy
What is bond energy?
the energy required to break the bond between two atoms
