Chemical Reactions Chemical reactions form new substances by breaking and making chemical bonds I.Chemical reactions alter arrangements of atoms A.Atoms interact in chemical reactions 1.Physical changes a.Some properties may change, but it’s still the same substance. 2.Chemical changes a.New substances are formed 1)Electrolysis- Water broken down into H 2 and O 2 2)Liquid H and liquid O in space shuttle combine to form H 2 O

3.Reactants and products a.Reactants- substances present at the beginning of a chemical reaction b.Products- substances formed by a chemical reaction c.The reactants CH 4 and O 2 form CO 2 and H 2 O 4.Evidence of Chemical reactions a.Some products look different than reactants b.Color Change- rust c.Formation of a precipitate- clam shell d.Formation of a gas (could be bubbles) e.Temperature change (+ or -) 1)Mg burning 2)Warm concrete 3)“Ice” pack

B.Chemical reactions can be classified 1.Synthesis- combination of simpler reactants to more complex products 2.Decomposition- More complex reactants break down into simpler products 3.Combustion- One reactant is always oxygen and another is often C or H - burning

C.The rates of chemical interactions can vary 1.Concentration- The number of particles present in a certain volume 2.Surface area- breaking a substance into smaller parts allows more particles to react at the same time 3.Temperature- Particles move faster or slower allowing more particles to react in a shorter amount of time 4.Catalyst- Not consumed or changed a.Like a matchmaker 5.All affect how many particles can interact at the same time