energy changes Flashcards
what is an exothermic reaction
- when a gas is released during a reaction
- heat energy is released into the environment
- the internal temp of the reaction is decreasing while the external is increasing due to release of thermal energy
what is an endothermic reaction
- heat is absorbed from environment into the reaction
- the internal temp of the reaction is increasing whilst the external temp is decreasing due to the absorption of thermal energy
examples of exothermic reactions
- chemical hand and body warmers
- self heating cans
- combustion
examples of endothermic reactions
- cold packs
- melting
- photosynthesis
how do cold packs work
- most cold packs contain ammonium nitrate or water
- ammonium nitrate dissolves and absorbs energy from surrounding making them colder
- only work for about 20 mins and not reusable
how do hot packs work
- crystallisation of a supersaturated solution is used in reusable warmers
- single use warmers tend to last for longer
what are reaction profiles
they show the relative amounts of energy contained in the reactants and reactants
reaction profile - exothermic
reactants line is higher than the products line
reaction profile - endothermic
reactants line is lower than the products line
what is the activation energy
the minimum amount of energy needed to cause/ start a reaction
how is activation energy shown in a reaction profile
arrow starting at reactants line and ending at the peak (pointing upwards)
bond breaking and making
- chemical bonds are broken when energy is absorbed (endothermic)
- chemical bonds are made/ formed when energy is released (exothermic)
what is bond energy
the energy needed to break bonds between atoms
bond energy calculations
list of bond energy for individual bonds are given, add to find total
