Exothermic and Endothermic Flashcards
chemical energy of a substance
the sum of its potential energy and kinetic energy
potential energy
energy stored in bonds between atoms
kinetic energy
energy of movement of atoms and molecules
what causes potential and kinetic energy
replusions between nuclei, repulsions between electrons, movement of electrons, vibrations and rotations around bonds
exothermic reactions
when the total amount of chemical energy of the products is less than the reactants, energy is lost to the surroundings, overall thermal energy from the environment is converted to chemical energy
what is the delta H value for exothermic reactions
negative
what type of reactions are exothermic
when bonds are made as this releases energy, combustion reactions
endothermic reactions
when the total amount og chemical energy of the products is greater than the reactants, energy is absorbed from surroundings, overall chemical energy is converted to thermal energy
what is the delta H value in endothermic reactions
positive value
what type of reactions are endothermic
when more energy is required to break the bonds than that gained from making new bonds
enthalpy
the chemical energy of a substance or its heat content, given the symbol H
molar enthaply
the amount of energy absorbed or released per mol of reactant, KJ mol-1
how is enthalpy changes for mictures measured
is KJ g-1
what is changes or delta H measured in
KJ
activation energy
the minimum amount of energy required to break bonds in reactants and initiate the reaction, given the symbol Ea
when is activation energy required
regardless if it is exothermic or endothermic as some energy must always first be absorbed to break the bonds holding reactant molecules together
what does the size of activation energy affect
the rate of reaction
activation energy in exothermic reactions
smaller as the reactants are higher in emergy
actiavtion energy in endothermic reactions
smaller as reactants are lower in energy
how do catalysts increase the rate of reaction
by decreasing Ea, so more particles are able to collide with sufficient energy to react under the lower Ea, so more frequent collisions occur, leading to a faster rate of reaction
changes of state
a type of physical change that involves energy being absorbed or released
what changes of state are exothermic
condensing a gas to a liquid and freezing a liquid to a solid as they both release heat to surroundings
what changes of state are endothermic
melting ice and boiling water as energy is absorbed (to break intermolecular forces)
