rates of chemical change Flashcards
key features of a chemical change
Formation of one or more different kinds of matter through a chemical reaction
new matter is formed
Changed cannot generally be undone or reversed
key features of a conservation mass
Matter is neither created nor destroyed
Atoms are rearranged in a chemical reaction. They are never ‘lost’
what is the collision theory of reactions
A chemical reaction occurs when:
Collisions between molecules have sufficient energy to break the bonds of reactants
Molecules collide with the proper orientation
Bonds between the atoms of the reactants are broken and new bonds form
characteristics of a chemical change:
Gas production
Colour change
Energy release – heat, light, sound
Energy absorbed
Solid forms (precipitate)
what is a chemical change?
the reactions forms new products
what is a physical change?
changes form but not chemical identity
what is the reaction rate?
Reaction rate is a measure of how quickly a chemical reaction occurs
(NOT how much product is made
what increases the reaction rate?
Increasing temperature
Increasing surface area of reactants
Increasing concentration of reactants
Increasing the pressure that the reaction occurs at (for gases)
Agitation
Catalysts
why are reactions faster at a higher temp?
Particles move faster at higher temperatures
Higher moving particles collide more often and there are more chances of particles to react
why are reactions faster when the surface area is increasing?
Any reaction involving a solid can only take place at the surface
Cutting the solid into several pieces will increase the surface area
Increased surface area will increase the number of reactants that can collide
More collisions means more reactions
why are reactions when there is an increasing concentration of reactants?
Concentration refers to the amount of solute in a solution
This means there are more particles, and a higher chance of reactions
Increasing the pressure in gases means more particles are closer together to collide – meaning higher chance for particle collisions
why are reactions faster when agitation occurs?
Agitation refers to mixing or shaking
The more a solution is mixed, the higher the chance of particle collisions, and reactions
why are reactions faster when a catalyst is there?
are all catalysts enzymes?
A catalyst is a substance that can seed up a reaction but is NOT consumed
A catalyst is not a reactant because they are not changed in the reaction
Enzymes are examples of biological catalysts but not all catalysts are enzymes
what are the two ways energy can transfer?
endothermic and exothermic
characteristics of exothermic
Transfer heat to their surroundings
Reaction mixture and surrounding become hotter
Examples include:
Burning (combustion)
Neutalisation reactions between acids and bases
Reaction between water and calcium oxide
