Describe the “scientific method” in terms of hypothesis, experiment, theory, and law. • The scientific method begins with observation (a woodpecker is make a hole in a tree). • Followed by hypothesis (because the tree has termites) • Followed by experiment (a collection of woodpeckers is observed in a setting in which trees have no termites). • Leading to a refined hypothesis and further experiment to a possible theory (woodpeckers only make holes when making a nest) • Leading to a “law” (if many additional observations cannot refute the theory).
State the Law of Conservation of Mass and use it to determine unknown masses of reactant or product in a chemical reaction. • In chemical reactions, atoms are neither created nor destroyed so that the mass of the reactants must equals the mass of the products. [pic]
How many grams of KCL must be formed?
Distinguish between, define, and give an example of physical change and chemical change. • In a physical change, no new substances are formed; no internal chemical bonds break and reform; only the physical state changes. [pic]
o The water molecule [pic] is structurally the same
o [pic] are endothermic physical changes
• In a chemical change, new compounds or elements forms due to breaking and forming chemical bonds. [pic]
o Exothermic chemical change
Distinguish between a physical property and a chemical property and give examples for each. • Physical properties include density, melting point, and other measurements related to the physical state. o Na is a soft solid at solid at room temperature
• Chemical properties relate to chemical reactivity, gaining or losing electrons, acidity, etc. o Na reacts with H2O at room temperature
o F2 is a better oxidizing agent than O2
o Cl has a higher electron affinity than F
o HCl is a stronger acid than HF...