Ivy Science Study Guide 2024 Fall Semester Test PDF

# Semester Test Fall 2024 Study Guide ## Phase Change ### Vocabulary - Phase - Molecule - Freedom of Movement - Kinetic energy - Molecule - Refute - Scale - Temperature - Molecular attraction ### Key Concepts - A solid keeps its shape because its molecules only move in place, not around each othe...

# Semester Test Fall 2024 Study Guide ## Phase Change ### Vocabulary - Phase - Molecule - Freedom of Movement - Kinetic energy - Molecule - Refute - Scale - Temperature - Molecular attraction ### Key Concepts - A solid keeps its shape because its molecules only move in place, not around each other. - A liquid can flow because its molecules move around, not away from each other. - A gas does not have a visible shape because its molecules can move away from each other. - A phase change is when the molecules that make up a substance experience a change to their freedom of movement. This phase change involves a macroscale change in appearance. - A change that can be observed at the macroscale can be explained by a change at the molecular scale, which cannot be observed with the naked eye. - When energy is transferred to or from a substance, it can change the molecules' freedom of movement. - Temperature is a measure of the average kinetic energy of the molecules of a substance. - Transferring energy to a substance increases the kinetic energy of that substance's molecules. Transferring energy from a substance decreases the kinetic energy of that substance's molecules. - Whether or not a phase change occurs is determined by the interaction between the kinetic energy of the molecules and the attraction pulling the molecules together. - The molecular attraction of a substance never changes. - A phase change occurs when the kinetic energy increases enough to overcome the attraction between molecules. - A phase change occurs when the kinetic energy decreases enough so that the attraction between molecules pulls them together. - Different substances can have either weaker or stronger molecular attraction. ### Example question A student left a sealed jar of water outside her home. Water can be a solid, liquid, or gas. When she put it outside, the water was a solid. Twelve hours later, the water had changed phase and was a liquid. What happened to the water molecules? a. Before the student left, the molecules were moving in place. After, the molecules were moving around each other. b. Before the student left, the molecules were moving around each other. After, the molecules were moving away from each other. c. Before the student left the molecules were moving around each other. After, the molecules were moving in place. d. Before the student left, the molecules were moving away from each other. After, the molecules were moving around each other. ### Questions - How does temperature affect the speed of molecules? - How does transfer of energy into or out of a substance affect phase change? - If a substance's molecules have a weak molecular attraction does this make it easier for the substance to change phase? - If a substance has a strong molecular attraction does this make it easier or harder for the substance to change phase? - Molecules that "move in place" describe a _______. - Molecules that "move around each other" describe a _______. - Molecules that "move away from each other" describe a _______. - If kinetic energy increases, what happens to the molecules? ## Chemical Reactions ### Vocabulary - Atoms - Model - Property - Scale - Substance - Chemical reaction - Product - Reactant - Rearrange ### Key Concepts - Different substances have different properties. - Things that are too small (or too large) to see can be studied with models. - Substances have different properties because they are made of different groups of atoms. These groups vary in the type or number of atoms that make up the group. - Groups of atoms repeat to make up a substance. - During a chemical reaction, one or more starting substances (reactants) change into one or more different substances (products). - During a chemical reaction, atoms do not change from one type to another. - During a chemical reaction, atoms rearrange to form different groups of atoms. - During a chemical reaction all of the atoms that make up the reactants rearrange to form the products. - During a chemical reaction, atoms cannot be created or destroyed. ### The atom - The basic building blocks of ordinary matter. - The basic unit of a chemical element (for example, gold, oxygen, mercury). - An atom consists of 3 basic parts: protons, neutrons, and electrons (also called electron cloud). ### Structure of an Atom - It consists of a nucleus in the center, which contains protons and neutrons. - The electron cloud surrounds the nucleus and contains electrons. The rings are referred to as shells or orbitals. ### Protons - Positively charged subatomic particles. - Located inside the nucleus. - Included in the atom's mass. - 1 proton = 1 atomic mass unit (amu). - atomic number = number of protons. - Determine the element's identity. ### Neutrons - No electrical charge. - Located inside the nucleus. - Included in the atom's mass. - 1 neutron = 1 atomic mass unit (amu). - The number of neutrons may not always be the same as the number of protons. ### Electrons - Negatively charged subatomic particle. - Located outside the nucleus. - Does not contribute to the atom's mass. - 1 electron = 1/2000 atomic mass unit (amu). - In a neutral atom, the number of electrons is the same as the number protons. ### Periodic Table - This table shows all the different elements there are on Earth. - It's called the Periodic Table of Elements. - Remember, an atom is the smallest unit of an element. - The formula for finding atomic mass is: # of protons + # of neutrons = mass number - The formula for finding the number of neutrons is: atomic mass - # of protons = # of neutrons. ### Balancing Chemical Equations - Subscripts describe the number of atoms in a molecule. - The coefficient represents the number of molecules. - H₂O - The subscript 2 represents 2 hydrogen atoms. - 2 H2O - The coefficient represents 2 molecules of H2O. ### Chemical Equation - Broken into three main parts: reactants, arrow, products. - 2H2+O2→2 H₂O - Reactant → Product - Arrow - Elements or compounds which exist prior to a chemical reaction (left of the arrow). - New substances (elements or compounds) that are created by the rearranging of atoms after a chemical reaction (right of the arrow). — The arrow represents a chemical reaction. In chemistry, as we read the equation, the arrow is read as "yields". — Atoms are rearranged to form new substances. — Atoms are not created or destroyed; they must be equal on both sides of the arrow. ### Law of Conservation of Mass - Matter (atoms) can not be created or destroyed. - Atoms are only rearranged.