chemical reactions Flashcards
chemical reactions
when particles collide and are rearranged to form new particles. chemical reactions involve energy changes.
as the reactant particles are rearranged, the chemical energy of the reactants is changed also.
energy can be absorbed or released
chemical energy
stored in chemical bonds between atoms and molecules. energy results from:
attractions between electrons and protons
repulsion between nuclei
repulsion between electrons
movement of electrons
vibration and rotation around bonds
law of conservation of energy
states energy cannot be created or destroyed.
chemical energy stored in a substance reduce and the energy must go elsewhere
a substance can’t gain in chemical energy without absorbing that energy from another source
system
the chemical reaction
refers to energy changes that occur as bonds and formed between the atoms of the elements involved in the reaction
surroundings
everything but the chemical reaction
energy goes from the surrounding to the reaction or energy is released into the surroundings
energy changes
the reactants in a reaction have a certain amount of energy in bonds, since the products are a rearrangement of the particles so they have different bonds and thus different amount of energy
for particles to separate,
energy is required, the separated articles have more energy than when they were together. particles coming together the products will have less energy than the separate particles, this lost energy is transferred to the surroundings
specific heat capacity
energy needed to change temperature of 1kg of a substance by 1 degree
exothermic
energy of products is less than energy of reactants and the lost energy is transferred to its surroundings
endothermic
when energy of the products is greater than the energy of the reactants
energy is absorbed from the surroundings
melting/boiling
endothermic
freezing
exothermic
enthalpy
stored chemical energy of a substance
activation energy
energy required to break the bonds of reactants so that a reaction can proceed
energy barrier that must be overcome before a reaction can start
unless this minimum energy amount is met, reactants rebound and move away from each other without reacting
combustion
the release of chemical energy when the fuel is burnt in the presence of oxygen
exothermic
complete combustion
when oxygen is plentiful and products are carbon dioxide and water
incomplete combustion
when oxygen supply is limited
not all carbon can be converted into carbon dioxide so carbon monoxide and or carbon is produced instead
energy content of fuels
heat of combustion of a fuel is defined as enthalpy change when a specified amount of fuel burns completely in oxygen
energy content: chemical energy available from a substance
fuels have high energy contents
factors that affect reaction rates
surface area of solid reactants concentration of reactants in a solution gas pressure Temperature presence of catalysts
rate of reaction
change in concentration of a reactant or product per unit time
need to measure amount of product being formed or amount of reactants being used up in a given ti8me period
depends on activation energy
magnitude of activation energy determine how easy it is for a reaction to occur and what proportion of collisions result in a successful reaction
collision theory
for collision theory to occur reactant particles must
collide with each other
collide with each other with sufficient energy to break bonds between the reactants
collide with the correct orientation to break the bonds between reactants and so allow formation of new products, if not correct orientation, particles bounce off each other
transition state
a new arrangement of atoms when activation energy is absorbed
occurs at the stage of maximum potential energy in the reaction (activation energy)
bond breaking and forming occur at this stage and arrangement of atoms is unstable
increase reaction rate
increasing a number of collisions that can occur in a given time
increasing proportion of collisions with an energy equal or greater than the activation energy
increasing frequency of collisions
increasing concentration of reactants (increasing pressure increase concentration)
increasing surface area of a reactant (more particles, more exposed surfaces of particles )
increase pressure
increasing energy of reactions
increasing temperature
catalyst lower activation energy required
