CHMY 121in 1st Edition Lecture 3Unit 3 ★ Chemical Reactions○ where bonds are broken and new materials are formed■ Reactants→ Products○ Synthesis Reaction■ A+B→ AB○ Decompostions■ AB→ A+B○ Single Replacement■ AB+C→ AC+B○ Double Displacement■ AB+CD→ AC+BD★ How Do Reactions Happen?○ Consider a reaction between Hydrogen and Solid Iodine■ nothing happens when they are mixed ○ How do they break apart?■ Covalent bonds are the strongest bonds but when you increase the heat itincreases movement which cause hydrogen and iodine to separate○ IT ALWAYS TAKES ENERGY TO BREAK A BONDAnnouncements● No class friday● Exam II answers will be posted on D2L ● Question 12 will be correct for everyone it was meant to read trigonal planar● Spring Break next week● HW 6 will open friday but isn't due until MArch 23rd ● Lecture 20 will be on D2L with quiz for clicker points★ Balancing Equations○ Law of conservation of matter■ same number of atoms in reactants as products○ starting with unbalanced reactions and add coefficients in front of the reactants tobalance the number of atoms○ Never change the subscripts★ Solubility & Precipitations○ Ionic compounds are often called salts■ many salts dissolve in water○ We can mix aqueous salts○ Precipitation when 2 aqueous solutions react and form a solid★ Writing Precipitation