Gwnls Final Exam 9th Science Dec 2013

The given equation represents a single displacement reaction because one element (C) is displacing another element (A) in the compound AB to form a new compound CB. This type of reaction occurs when a more reactive element displaces a less reactive element in a compound.

A radical is not a particle of an atom. It is a group of atoms that contains an unpaired electron and is highly reactive. Protons, neutrons, and electrons are the three main particles that make up an atom. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. Therefore, the correct answer is Radical.

Boiling is not a potential sign of chemical change because it is a physical change, not a chemical change. Boiling occurs when a substance reaches its boiling point and changes from a liquid to a gas, but the chemical composition of the substance remains the same. In contrast, the other options - change in odor, fizzing, and change in color - can all indicate a chemical change, as they suggest a transformation in the chemical properties or composition of a substance.

The mass number of an atom is the total number of protons and neutrons in its nucleus. Electrons, on the other hand, have a negligible mass compared to protons and neutrons and do not significantly contribute to the mass number. Therefore, the correct answer is "protons and neutrons."

All of the given options, dissolving, evaporating, and bending, are examples of physical changes. A physical change refers to a change in the physical properties of a substance without altering its chemical composition. Dissolving involves the solute particles dispersing in a solvent, evaporating refers to the change of a liquid into a gas, and bending refers to the change in shape or form of an object without any chemical reaction taking place. Therefore, all of these options demonstrate physical changes.

In a balanced chemical equation, the reactants must equal the products. This means that the number of atoms of each element on both sides of the equation must be the same. This is because of the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. Therefore, in order for the equation to be balanced, the reactants and products must have the same number of atoms of each element.

When an object floats on a fluid, it means that the object is able to stay on the surface of the fluid without sinking. This can only happen if the object is less dense than the fluid it is floating on. Density is a measure of how much mass is packed into a given volume. If the object is less dense than the fluid, it means that it has less mass packed into the same volume compared to the fluid. This allows the object to displace a volume of fluid equal to its own weight, causing it to float.

Valence electrons are the electrons in the outermost energy level of an atom. These electrons are important because they determine the chemical properties and reactivity of an element. Valence electrons are involved in chemical bonding and can be shared, gained, or lost in order to achieve a stable electron configuration. Therefore, the correct answer is "The electrons in the outermost energy level."

Sublimation is the process in which a solid directly turns into a gas without going through the liquid phase. This occurs when the temperature and pressure conditions are such that the solid particles have enough energy to break free from their fixed positions and enter the gas phase. Examples of substances that undergo sublimation include dry ice (solid carbon dioxide) and mothballs (solid naphthalene). Therefore, sublimation is the correct answer for the process of a solid becoming a gas.

Condensation is the correct answer because it refers to the process of a gas, such as water vapor, cooling down and changing into a liquid state. This occurs when the gas loses heat energy and its molecules come together to form liquid droplets. Condensation commonly happens when warm air cools, such as when water vapor in the air turns into water droplets on a cold surface, like windows or mirrors.

Decreasing the temperature does not speed up a chemical reaction. In fact, lowering the temperature slows down the reaction rate because it reduces the kinetic energy of the reactant molecules, making them less likely to collide and react. Increasing the temperature, on the other hand, increases the kinetic energy of the molecules, causing them to move faster and collide more frequently, which speeds up the reaction. Adding a catalyst also speeds up a reaction by providing an alternative pathway with lower activation energy. Increasing the surface area exposes more reactant molecules to each other, leading to more frequent collisions and faster reaction rates.

According to Newton's second law of motion, the acceleration of an object is inversely proportional to its mass. This means that as the mass of a particle increases, its acceleration decreases. Since speed is directly related to acceleration, a heavier particle will move slower.

A solid is the state of matter that has a definite shape and volume. In a solid, the particles are closely packed together and are held in a fixed position by strong intermolecular forces. This arrangement of particles gives solids a rigid structure, allowing them to maintain their shape and volume. Unlike liquids or gases, solids do not flow or easily change their shape when subjected to external forces. Therefore, a solid is the correct answer as it is the only state of matter that exhibits both definite shape and volume.

Atoms have no charge because they have an equal number of protons and electrons. Protons have a positive charge, while electrons have a negative charge. Since the number of protons and electrons is the same in an atom, their charges cancel each other out, resulting in a neutral overall charge for the atom.

The dissolution of a material is not a sign of a chemical reaction because it is a physical process. Dissolving occurs when a solute is mixed with a solvent and forms a homogeneous mixture, without any chemical bonds being broken or formed. In a chemical reaction, new substances are formed with different chemical properties, and there is usually evidence of a reaction such as the release of gas, heat, or a color change.

According to Bernoulli's principle, an increase in speed of a fluid will result in a decrease in pressure. This principle is based on the conservation of energy, where an increase in fluid velocity is accompanied by a decrease in pressure. This can be observed in various scenarios, such as when air flows faster over the top of an airplane wing, resulting in lower pressure and lift. Therefore, the correct answer is "decreases."

Alkali metals are very reactive because they have one valence electron. Valence electrons are the outermost electrons in an atom, and they are involved in chemical bonding. Alkali metals only have one valence electron, which makes them highly reactive as they tend to lose this electron and form positive ions. This electron configuration creates a strong driving force for alkali metals to react with other elements and compounds in order to achieve a stable electron configuration.

Neutrons and protons are found in the nucleus of an atom. The nucleus is the central part of the atom that contains most of its mass. Neutrons are neutral particles, while protons have a positive charge. They are tightly packed together in the nucleus, forming the dense core of the atom. Electrons, on the other hand, orbit around the nucleus in specific energy levels or shells. Therefore, the correct answer is "in the nucleus".

The correct answer is Noble Gases. Noble gases are a group of chemical elements that are characterized by their low reactivity and full outer electron shells. They are located in group 18 of the periodic table. Unlike other elements, noble gases have stable electron configurations and do not readily form compounds with other elements. Some examples of noble gases include helium, neon, argon, krypton, xenon, and radon.

Viscosity is the correct answer because it refers to the resistance of a fluid to flow. Viscosity is a measure of a fluid's internal friction or resistance to shear forces. It determines how easily a fluid can flow and is influenced by factors such as temperature and the size and shape of particles in the fluid. A high viscosity fluid is thick and flows slowly, while a low viscosity fluid is thin and flows easily.

When two or more atoms chemically combine, they form molecules. Molecules are the smallest units of compounds and can be made up of the same type of atoms (elements) or different types of atoms. Larger atoms and protons are not formed by the joining of multiple atoms, hence they are not the correct options.

Reactivity is not a physical property because it refers to the ability of a substance to undergo a chemical reaction. Physical properties, on the other hand, are characteristics that can be observed or measured without changing the substance's chemical composition. Color, shape, and density are all physical properties as they can be observed or measured without altering the substance's chemical makeup.

Breaking chalk is a physical change, not a chemical change. When chalk is broken, its physical state is altered, but the chemical composition of the chalk remains the same. No new substances are formed during the process of breaking chalk. Therefore, the correct answer is false.

Gases do not have a definite shape or volume. Unlike solids and liquids, gases can expand to fill the space available to them. They take the shape and volume of their container. Therefore, the statement that gases have a definite volume is incorrect.

Isotopes of an element have the same number of protons (atomic number) but different numbers of neutrons. Since the question states that the two isotopes of Hydrogen are different, it implies that they have different numbers of neutrons. The number of electrons and atomic numbers remain the same for isotopes of an element.

The periodic table organizes elements into groups based on their properties. This allows for easier identification and classification of elements with similar characteristics. By grouping elements with similar properties together, scientists can make predictions about the behavior and reactivity of elements within a group. This organization is based on the observation that elements in the same group tend to have similar electron configurations and therefore exhibit similar chemical properties.

Potassium, being an alkali metal, is highly reactive because it has one electron in its outer energy level. This electron is loosely held and easily lost, making potassium prone to react with other elements to achieve a stable electron configuration. This reactivity is a result of the tendency of atoms to gain or lose electrons in order to attain a full outer energy level, which is a more stable state.

Chemical bonds are the forces that hold atoms together. These bonds are formed when atoms share, donate, or accept electrons to achieve a stable electron configuration. This sharing or transfer of electrons creates a strong attraction between the atoms, resulting in the formation of molecules or compounds. Unlike electric currents or physical bonds, which are not specifically involved in holding atoms together, chemical bonds are responsible for the stability and structure of matter. Nuclear forces, on the other hand, are responsible for holding the nucleus of an atom together and are not directly involved in holding atoms together in molecules.

Each molecule of sugar (C12H22O11) contains 12 atoms of carbon. This is because the chemical formula of sugar indicates that there are 12 carbon atoms present in each molecule. The number in front of the element symbol (C) represents the number of atoms of that element in the molecule. Therefore, the correct answer is 12 atoms of carbon.

When two chlorine atoms bond and share a pair of electrons evenly, the bond is called a nonpolar covalent bond. In a nonpolar covalent bond, the electrons are shared equally between the two atoms, resulting in no separation of charge or polarity. Since chlorine atoms have the same electronegativity, they have an equal pull on the shared electrons, causing the bond to be nonpolar.

Soil is a mixture because it is composed of various organic and inorganic materials such as minerals, water, air, and organic matter. These components are not chemically combined and can be separated physically. Therefore, soil is considered a heterogeneous mixture.

Atoms form bonds to become more stable. When atoms bond, they share, gain, or lose electrons to achieve a more stable electron configuration. This stability is achieved by filling or emptying their outermost energy levels, which allows the atoms to have a full valence shell. By becoming more stable, atoms decrease their energy and increase their overall stability.

When ice melts to form water, energy is absorbed. This is because the process of melting requires heat energy to break the bonds between the water molecules in the solid ice and convert them into liquid water. The absorbed energy increases the kinetic energy of the water molecules, causing them to move more freely and transition from a solid to a liquid state.

Metallic bonds allow copper to bend and conduct electricity because they involve the delocalization of electrons in a metal lattice. This delocalization allows the electrons to move freely throughout the lattice, making metals malleable and allowing them to be bent without breaking. Additionally, the delocalized electrons can easily carry electric current, making metals good conductors of electricity.

The correct answer is "Copper (II) oxide" because the compound contains copper ions with a charge of +2, which is indicated by the Roman numeral II in parentheses. The compound also contains oxygen, so it is named as copper (II) oxide.

Carbon is the element that is found in all organic compounds. Organic compounds are compounds that contain carbon atoms bonded to other carbon atoms, as well as other elements such as hydrogen, oxygen, and nitrogen. Carbon is unique in its ability to form stable bonds with other carbon atoms, allowing for the formation of complex and diverse organic molecules. Therefore, carbon is a fundamental element in organic chemistry.

In a liquid, the particles are closely packed together but still have enough energy to slide past each other. This allows the liquid to flow and take the shape of its container.

A fluid is defined as a substance that can flow and take the shape of its container. Gas, air, and liquid are all examples of fluids because they can flow and take the shape of their containers. However, marshmallow is not a fluid because it cannot flow and does not take the shape of its container. Marshmallows are solid and have a fixed shape.

This statement is based on the law of conservation of mass, which states that in a closed system, the total mass remains constant over time. This means that matter cannot be created or destroyed, only transformed or rearranged. This principle is a fundamental concept in chemistry and physics, and it has been experimentally observed and verified in various scenarios. Therefore, the correct answer is true.

The symbol for Hydrogen is H. This is a true statement. In the periodic table, each element is represented by a symbol, and for Hydrogen, the symbol is H.

When gas is at a constant volume, an increase in temperature would cause an increase in pressure. This is because an increase in temperature leads to an increase in the average kinetic energy of gas molecules. As the molecules move faster and collide more frequently with the walls of the container, they exert a greater force on the walls, resulting in an increase in pressure.

The symbol for Oxygen is indeed O. In chemistry, symbols are used to represent elements, and O is the symbol assigned to Oxygen.

The symbol for Chlorine is Cl, not Ch. The symbol for an element is a shorthand representation of its name, usually derived from the first one or two letters of the name. In the case of Chlorine, the symbol is Cl, which accurately represents its name. Therefore, the statement "The symbol for Chlorine is Ch" is false.

The symbol for Gold is Au. This is a true statement. In the periodic table, each element is represented by a unique symbol, and the symbol for gold is Au. The symbol "Au" comes from the Latin word for gold, "aurum." It is widely recognized and used by scientists and chemists to denote gold in various contexts.

The symbol for Iron is actually Fe, not Ir. Ir is the symbol for Iridium, another element on the periodic table.

In a combustion reaction, water is always produced as a product. Combustion reactions involve the reaction of a fuel with oxygen to produce heat and light. During this process, carbon-based fuels (such as hydrocarbons) react with oxygen to form carbon dioxide and water as the main products. Since water is a byproduct of combustion reactions, it is always present in the reaction. Carbon, carbon monoxide, and glucose may also be involved in combustion reactions, but water is consistently produced.

In a chemical reaction, atoms are rearranged. This means that the arrangement of atoms in the reactants is changed to form new products. The bonds between atoms are broken and new bonds are formed, resulting in a different arrangement of atoms. However, no atoms are destroyed or created in a chemical reaction, as atoms are conserved. The total number of atoms remains the same before and after the reaction, only their arrangement is altered.