Energy from Reactions Flashcards
what is an exothermic reaction
when heat energy is given out to surroundings
how do we know its an exothermic reaction
rise in temperature
what happens to the energy of the products in an exothermic reaction
they have less energy than the reactants
what is activation energy
minimum amount of energy needed by the reactant particles to react on collision
what are some examples of exothermic reactions
combustion of fuels
neutralisation reactions
displacement reactions
respiration
what is an endothermic reaction
when heat energy is taken in from the surroundings
how do we know it is an endothermic reaction
drop in temperature
what happens to the energy of the products in an endothermic reaction
they have more energy than the reactants
what are some examples of endothermic reactions
electrolysis
cracking
photosynthesis
what does a catalyst do
it provides an alternative reaction route that requires a lower activation energy. This speeds up the reaction because more of the reactant particles have enough energy to react on collision, so more successful collisions will occur
what does it mean if the reaction is slow at room temperature
the reaction has a high activation energy
why might one reaction take place faster than another is both are carried out under the same conditions
activation energy for one reaction is lower, so more of the reactant particles can react on collision
is bond breaking endothermic or exothermic
endothermic, as energy is needed to break the bonds in the reactants
is bond forming endothermic or exothermic
exothermic
explain in terms of bond breaking and making why the reaction is exothermic
more energy is released when bonds are formed in the products than is needed to break bonds in the reactants. Therefore the reaction is overall negative and hence exothermic
explain in terms of bond breaking and making why the reaction is endothermic
more energy is needed to break bonds in the reactants than is released when bonds are formed in the products. Therefore the reaction is overall positive and hence endothermic
why must energy be supplied to start a reaction but it continues by itself once started
existing bonds must first be broken in the reactants before new bonds can form in the products. Bond breaking needs energy, whereas energy is released when new bonds are formed in the products. More energy is released when bonds are formed in the products, so the reaction is overall exothermic and provides the energy needed to break more bonds. Therefore the reaction continues
why is hydrogen good fuel to use in an aeroplane
hydrogen has a low density
it gives out heat energy when burnt
combustion product is water which is not harmful
Nickel sulphate water exists as bright green crystals and anhydrous nickel sulphate as a yellow powder.
How could you show that the action of heat on the hydrated salt is a reversible reaction
heat the green crystals in a test tube. The colour changes from green to yellow. Allow the test tube to cool, and then add water to the yellow powder. It turns green again.