Grade 8 Chapter 6 Physical Science

The correct chemical equation for the statement "Sodium reacts with oxygen in a 2 to 1 ratio to produce sodium oxide" is 2Na + O2 → Na2O. This equation correctly represents the reaction between sodium and oxygen, where two sodium atoms combine with one oxygen molecule to form sodium oxide.

A chemical equation that shows the same number of each kind of atom on both sides of the equation is said to be balanced. This means that the equation obeys the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. By having an equal number of atoms on both sides, the equation demonstrates that the reactants and products are in the correct proportions and that no atoms are lost or gained during the reaction.

Matter is defined as anything that has mass and occupies space. It includes both solid, liquid, and gas forms. Energy, on the other hand, refers to the ability to do work or cause a change. Chemistry is a branch of science that deals with the composition, properties, and behavior of matter. Endothermic, on the other hand, refers to a process or reaction that absorbs heat from its surroundings. Therefore, the correct answer is matter.

When chemical bonds break and new bonds form, it indicates a chemical change. In a chemical change, the substances involved undergo a rearrangement of their atoms, resulting in the formation of new substances with different properties. This process involves the breaking and formation of chemical bonds, which requires energy. Therefore, the correct answer is a chemical change.

In an open system, matter can enter from or escape to the surroundings. This means that during a chemical reaction, substances can be added to the system or removed from it. This allows for the exchange of matter with the surroundings, which can affect the progress and outcome of the reaction. It is important to consider this when studying or analyzing chemical reactions in open systems.

The correct answer is "the study of matter and how matter changes." This is because chemistry is a scientific discipline that focuses on understanding the properties, composition, structure, and behavior of matter. It involves studying the different forms of matter, such as solids, liquids, and gases, and how they interact and undergo various changes, such as chemical reactions and phase transitions. Chemistry also explores the principles and laws that govern these changes and the ways in which matter can be manipulated and utilized for various purposes.

An endothermic reaction is a chemical reaction that absorbs energy in the form of heat. This means that the reactants in the reaction require an input of heat energy in order to proceed and form the products. The energy absorbed is usually taken from the surroundings, causing a decrease in temperature. In contrast, an exothermic reaction releases energy in the form of heat, combustion refers specifically to a reaction with oxygen that produces heat and light, and unbalanced refers to a reaction that does not have an equal number of atoms on both sides of the equation.

A chemical equation is a shorter and easier way to represent chemical reactions using symbols instead of words. It provides a concise representation of the reactants and products involved in the reaction, as well as the stoichiometry or the ratio of their quantities. This allows scientists to easily understand and communicate the reaction without the need for lengthy descriptions. Chemical equations are an essential tool in chemistry for studying and analyzing various chemical processes.

The principle of conservation of matter states that matter cannot be created or destroyed in a chemical reaction. This means that the total mass of the reactants must be equal to the total mass of the products. In other words, the amount of matter before the reaction is the same as the amount of matter after the reaction, even though the form or arrangement of the matter may change. This principle is a fundamental concept in chemistry and is supported by the law of conservation of mass.

A synthesis reaction is a process where multiple substances combine to form a single, more complex substance. On the other hand, a decomposition reaction is the opposite process where a complex substance breaks down into simpler substances. Therefore, a synthesis reaction and a decomposition reaction can be considered opposites as they involve opposite chemical processes.

The number placed below an element's symbol in a chemical formula is called a subscript. Subscripts are used to indicate the number of atoms of each element in a molecule or compound. They are written in small font and are positioned slightly below and to the right of the element's symbol. Subscripts are essential for accurately representing the composition of a chemical formula and determining the ratio of elements in a compound.

The given answer states that "The reaction is a physical change" which is not a correct inference about the burning of gasoline. When gasoline burns, chemical bonds are broken and others are formed, new substances are produced, and energy is released. Therefore, the burning of gasoline is a chemical reaction, not a physical change.

Enzymes are chemicals that act as biological catalysts by speeding up reactions in living things. They work by lowering the activation energy required for a reaction to occur, thus increasing the rate of the reaction. Unlike inhibitors, which slow down or prevent reactions, enzymes facilitate and enhance the efficiency of biochemical reactions. Fuels and reactants are not specifically involved in catalyzing reactions in living organisms.

A bottle of hydrogen peroxide that eventually turns into a bottle of water and oxygen gas is an example of a decomposition reaction. In a decomposition reaction, a compound breaks down into simpler substances. In this case, the hydrogen peroxide molecule (H2O2) breaks down into water (H2O) and oxygen gas (O2).

The production of one or more new substances is the only sure evidence for a chemical reaction. This is because in a chemical reaction, the reactants undergo a rearrangement of atoms to form new products with different chemical properties. While the formation of a gas, a color change, or changes in properties may also indicate a chemical reaction, they are not always definitive evidence as they can occur in physical changes as well. Therefore, the production of new substances is the most reliable indicator of a chemical reaction.

In a chemical equation, the substances listed on the left side are the reactants. Reactants are the starting materials or substances that undergo a chemical reaction to form new substances called products. This reaction is represented by the chemical equation, where reactants are written on the left side and products on the right side. The reactants are the substances that are consumed or used up during the reaction, and their chemical bonds are rearranged to form the products.

In a double displacement reaction, the cations and anions of two different compounds switch places, resulting in the formation of two new compounds. In this reaction, FeS reacts with HCl to form FeCl2 and H2S. The Fe cation from FeS combines with the anion Cl from HCl to form FeCl2, while the anion S from FeS combines with the cation H from HCl to form H2S. Therefore, this reaction is a double displacement reaction.

The correct answer is "formula" because CaCO3 represents the chemical formula for calcium carbonate. A chemical formula is a shorthand representation of the elements present in a compound and the ratio of their atoms. In this case, CaCO3 indicates that calcium (Ca) is combined with carbon (C) and oxygen (O) in a specific ratio.

The numbers that appear in front of a chemical formula in a chemical equation represent the number of molecules or atoms of each substance involved in the reaction. These numbers, known as coefficients, are used to balance the equation and ensure that the same number of atoms of each element are present on both sides of the equation. By indicating the number of molecules or atoms, these coefficients help to determine the stoichiometry of the reaction, allowing for accurate calculations of the amounts of reactants and products involved.

The equation 2Fe2O3 + 3C --> 4Fe + 3CO2 is a balanced equation because the number of atoms of each element is the same on both sides of the equation. There are 8 iron atoms, 6 oxygen atoms, and 3 carbon atoms on both sides of the equation, satisfying the law of conservation of mass.