energy changes Flashcards
what is the law of conservation?
energy cannot be created or destroyed and can only be converted from one form to another
what is an exothermic reaction?
energy is given out to the surroundings
what are examples of physical process of exothermic changes?
condensation, freezing, dissolving concentrated sulfuric acid
what are chemical reactions of exothermic changes?
combustion, neutralisation, corrosion of metals, respiration, reactions in simple/electric cells
how does the temperature change in an exothermic change?
temperature increases than reaches a maximum and then drops until it reaches room temperature
what is an endothermic reaction?
a reaction where energy is taken in from the surroundings
what are physical examples of endothermic changes?
melting, boiling, sublimation, dissolving of ammonium salts in water
what are chemical examples of endothermic changes?
photosynthesis, thermal decomposition of compounds, action of light on silver bromide in photographic film, electrolysis
what is an enthalpy change/heat of reaction?
the amount of heat energy given out or taken in during a chemical reaction
what is the unit for enthalpy change?
kilojoules
what is the formula for enthalphy change?
total energy of products - total energy of reactants
what does the energy level for exothermic reaction look like?
as reactants give out heat energy tot he surroundings,.the energy of products is lower than energy of the reactants
what is the energy like in the exothermic reaction?
Hproducts < Hreactants, enthalpy change is negative
what is activation energy?
the minimum amount of energy that the reactants must possess in order for a chemical reaction to occur
what happens when reactant particles have energy less than activation energy?
no reaction occurs
what kind of process is bond breaking?
an endothermic process
what kind of process is bond forming?
an exothermic process
what is the formula for overall enthalpy change?
total energy for bond breaking - total energy for bond forming
how is an exothermic process related to bond breaking/bond forming?
total energy absorbed for bond breaking < total energy released for bond forming
how is an endothermic process related to bond break/bond forming?
total energy absorbed energy for bond breaking > total energy released for bond forming
how is energy in breaking a covalent bond related to energy given out in forming a covalent bond?
energy absorbed in breaking a covalent bond is the same as energy given out in forming a covalent bond
what are fuels?
substances that can burn easily in air to give out energy
what are the benefits of using hydrogen as fuel?
does not cause pollution + renewable source of energy + efficient source of energy
what are the disadvantages of hydrogen as fuel?
no cheap sources of hydrogen + extremely flammable and explosive + requires larger storage volumes compared to other fuels
