Presentation on theme: "Chapter 8 Chemical Reactions. A chemical reaction is a process in which the physical and chemical properties of the original substances change as new."— Presentation transcript:
Chapter 8 Chemical Reactions
A chemical reaction is a process in which the physical and chemical properties of the original substances change as new substances with different physical and chemical properties are formed
Law of Conservation of Mass During a chemical or physical change, all mass remains the same. Mass is neither created nor destroyed.
Parts of a chemical reaction coefficientsubscript coefficient Subscript tells the # of atoms in molecule Coefficient tells # of molecules in reaction 2 H 2 + O 2 2 H 2 O
Parts of a chemical equation reactant product Reactant is what goes into a chemical reaction Product is what results in the reaction 2 H 2 + O 2 2 H 2 O
Capacity to react The ease with which atoms will form bonds is its bonding capacity. This capacity is directly related to the electrons and their placement and number within the energy levels.
What happens when a chemical reaction occurs? 1.Atoms can form molecules 2.Molecules can break apart to form atoms 3.Molecules can react with other molecules
Balancing Equations Start with the first atom on the reactants side Count the total number of atoms of the element on left and then on the right Add a coefficient in front of atom(s) or compounds where necessary Never change a subscript Go back through each atom and recheck and/or change until # are equal on both sides of the equation
Types of Chemical Reactions SYNTHESIS –2 or more substances combine DECOMPOSITION –complex substance breaks down SINGLE - REPLACEMENT –uncombined element replaces another element in a compound DOUBLE - REPLACEMENT –atoms of 2 compounds replace each other (a flip-flop)
synthesis Simple molecules or compounds combine to make a new and more complex substance 2 H 2 + O 2 2 H 2 O
decomposition A complex substance breaks down into simpler substances 2 H 2 O 2 H 2 + O 2
single-replacement Single element replaces another element within a compound 2Na + 2H 2 O 2NaOH + H 2
double-replacement Different atoms in two different compounds replace each other MgCO 3 + 2HCl MgCl 2 + H 2 CO 3
In any chemical reaction: -- some energy is needed to start the change -- some energy is involved during the reaction
ACTIVATION ENERGY is what is needed to get a reaction started Ex: striking a match
Energy involved in the reaction can be either: Exothermic or Endothermic
Exothermic energy is released during reaction the energy in the reactants are higher than the products ex means out therm means heat Ex: fireworks
Endothermic energy is absorbed during reaction the energy in the products are higher than the reactants endo means in therm means heat Ex: chemical ice
Kinetics Kinetics is the study of reaction rates In order to react, atoms must collide. In order for bonds to be broken, formed or reformed, particles must collide at precisely the correct angle with the proper amount of energy.
Four factors that influence the collision theory are... Rates of Chemical Reactions The more collisions, the faster the rate of the chemical reaction
concentration –the amount of reactants present surface area –amount of exposed material temperature –higher temperature causes atoms to display more energy & reaction rate is increased catalysts –increases speed by decreasing the activation energy needed, but does not enter the reaction –called enzymes in living organisms