sience unit 6

What is a covalent bond?

A covalent bond is formed between two atoms when they share one or more pairs of valence electrons.

What is an ionic bond?

An ionic bond is a bond formed between a cation and an anion after the transfer of valence electron(s) between them.

What do subscripts in a chemical formula indicate?

A subscript in a formula tells how many atoms of each kind are in a molecule and allows us to determine the ratio of atoms that combine in a compound.

What is the law of conservation of mass?

The law of conservation of mass states that the total mass before and after a physical change remains the same, even when the physical properties of matter change.

What are the signs of a chemical reaction?

Signs of a chemical reaction include a change in color, a change in temperature, the formation of gas bubbles, and the formation of a precipitate.

What is a synthesis reaction?

A synthesis reaction is a reaction in which two or more substances combine to form a single new substance.

What is a decomposition reaction?

A decomposition reaction is a reaction in which a compound breaks down into two or more simpler substances.

What is a single-replacement reaction?

A single-replacement reaction is a reaction in which one element replaces a similar element in a compound.

What is a double-replacement reaction?

A double-replacement reaction is a reaction in which the positive and negative ions of two ionic compounds exchange places to form two new compounds.

What happens in combustion reactions?

In combustion reactions, a substance (a fuel) reacts with an oxidant, usually oxygen, which releases energy.

What is the difference between endothermic and exothermic reactions?

Endothermic reactions absorb heat, while exothermic reactions release heat.

What is a catalyst?

A catalyst is a substance that can speed up a reaction without being used up in the process and lowers the activation energy.

What is cohesion?

Cohesion is the attraction of molecules for other molecules of the same kind, responsible for surface tension in liquids.

What is adhesion?

Adhesion is the attraction of molecules for molecules of a different kind.

What are intermolecular forces?

Intermolecular forces are attractive forces between two different substances, which are weaker and not part of the substance.

What is a hydrogen bond?

A hydrogen bond is a special type of intermolecular force that occurs between molecules containing polar covalent bonds, specifically involving a hydrogen atom bonded to a highly electronegative atom.

What is activation energy?

Activation energy is the minimal amount of energy necessary to initiate a chemical reaction.

What is an endothermic reaction?

An endothermic reaction is a chemical reaction that absorbs heat from its surroundings.

Example of an endothermic reaction:

The reaction of ammonium nitrate with water, which is used in instant cold packs, absorbs heat from the surroundings.

What is an exothermic reaction?

An exothermic reaction is a chemical reaction that releases heat to its surroundings.

Example of an exothermic reaction:

The combustion of methane (CH4 + 2O2 \rightarrow CO2 + 2H2O + \text{heat}) releases heat as a product.

What is a combustion reaction?

A combustion reaction is a process where a substance (often a hydrocarbon) reacts with oxygen, producing carbon dioxide and water, along with energy.

Balanced equation for the combustion of propane:

The balanced chemical equation for the combustion of propane is C3H8 + 5O2 \rightarrow 3CO2 + 4H_2O + \text{heat}.

What are the products of the combustion of hydrocarbons?

The products of the combustion of hydrocarbons are typically carbon dioxide (CO2) and water (H2O).

Example of a synthesis reaction:

A synthesis reaction is when two or more reactants combine to form a product, such as 2H2 + O2 \rightarrow 2H_2O (the formation of water from hydrogen and oxygen).

Example of a decomposition reaction:

A decomposition reaction occurs when a compound breaks down into simpler substances, such as 2H2O \rightarrow 2H2 + O_2 (the electrolysis of water).

What is a redox reaction?

A redox (oxidation-reduction) reaction involves the transfer of electrons between two species; oxidation is the loss of electrons, and reduction is the gain of electrons.

Example of a physical change:

Melting ice is an example of a physical change where water changes from solid to liquid without altering its chemical composition.

What is thermal decomposition?

Thermal decomposition is a type of decomposition reaction in which a compound breaks down into simpler substances when heated.

Example of thermal decomposition:

The thermal decomposition of calcium carbonate occurs when heat is applied: CaCO3 \rightarrow CaO + CO2.

What is a precipitation reaction?

A precipitation reaction is a type of chemical reaction where two soluble salts react in solution to form an insoluble solid called a precipitate.

Example of a precipitation reaction:

When barium chloride reacts with sodium sulfate, barium sulfate precipitates out: BaCl2 + Na2SO4 \rightarrow BaSO4(acq) + 2NaCl.

What are the characteristics of an exothermic reaction?

Exothermic reactions release energy in the form of heat and result in an increase in temperature of the surroundings.

What are the characteristics of an endothermic reaction?

Endothermic reactions absorb energy, usually in the form of heat, resulting in a decrease in the temperature of the surroundings.

Example of an oxidation reaction:

The reaction between iron and oxygen to form iron oxide (rust) is an example of an oxidation reaction: 4Fe + 3O2 \rightarrow 2Fe2O_3.

Example of a reduction reaction:

The reaction between copper(II) oxide and hydrogen gas, where copper(II) oxide is reduced to copper: CuO + H2 \rightarrow Cu + H2O.

What is a reversible reaction?

A reversible reaction is a chemical reaction where the reactants can form products, which can react to regenerate the reactants.

Example of a reversible reaction:

The synthesis of ammonia from nitrogen and hydrogen is a reversible reaction: N2 + 3H2 \rightleftarrows 2NH_3.