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8.1: Equations for chemical reaction:

when a chemical change occurs to a substance, it gets converted into one or more substances, creating a new product and this process is known as "chemical reaction."

you can track this chemical reaction by making a "chemical equation": presenting the "reactants" (written on the left of the arrow) and getting the "product" ( new product) (written on the right of the arrow).
If there was a symbol such as delta above the arrow , it means that heat was used in this reaction.

In any chemical reaction, atoms are conserved which means there is no loss, gain or share ... unchanged atoms.

Each chemical equation should be "balanced", However if there are more atoms in one of the reactants unlike the other , then we place a "coefficient" which is a whole number used to balance the equation.

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A physical change is a change in which no new substance is formed; a chemical change results in the formation of one or more new substances. Again, consider the previous examples: Freezing water into ice just results in water molecules which are 'stuck' together - it's still H2O. Whereas burning wood results in ash, carbon dioxide, etc, all new substances which weren't there when you started.

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1. A physical change is reversible, a chemical change is not. For example, the freezing of water would be a physical change because it can be reversed, whereas the burning of wood is a chemical change - you can't 'unburn' it

2. A physical change is a change in which no new substance is formed; a chemical change results in the formation of one or more new substances. Again, consider the previous examples: Freezing water into ice just results in water molecules which are 'stuck' together - it's still H2O. Whereas burning wood results in ash, carbon dioxide, etc, all new substances which weren't there when you started.

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In a physical change, only the physical features on the substance change. The chemical composition remains exaclty the same.
In a chemical change, the chemical compositions of the substances change, producing a new substance.

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Chemical tactiob

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-chemical reaction always involves a chemical change
- atoms form new combinations in reactions with new properties
- chemical equation tells us the materials we need and the products that will form
- reactants are on the left, products on right

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is a chemical because atoms of the reacting substances form new combinations with new propertied

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In order to know the definition of a chemical reaction, you need to know the difference between a chemical and a physical change. a chemical change occurs with a chemical reaction and

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A chemical reaction is when two substances react and make a new substance.

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A chemical reaction is where bonds are broken between reactants and formed between the products. It differs from a physical change as new atoms and compounds are formed.
The number of atoms doesn't change in a chemical reaction. The reaction has to be balanced between the reactants and products.

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- in a physical change, only the shape or size of a substance changes, but it's composition stays the same.
- in a chemical change, substances react with each other to produce entirely different compositions and properties. But all of the atoms of the original substances are still found in the newly formed substance.

-when a chemical reaction occurs, some of the bonds between the atoms in the original substances get broken and new ones form with different combinations of atoms, thus producing new substances

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Unlike physical reactions, that only change in features. A

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-A chemical reaction is when two substances react and make a new substance.

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CHEMICAL REACTIONS

When the appearance of a substance changes, but not its composition it is a physical change. Example : When tear a paper, only the size of the paper changes but it is still a paper.

When a substance changes into a new substance that have different composition and different properties it is a chemical change. Example : when we burn a paper it doesn't stay as paper it turns to ash.

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1. A chemical reaction is when two substances' atoms react to form new combination of atoms and new substances with different properties from the original.
2. The materials, or in this case, the substances needed for a chemical reaction, and the result are known to us from the chemical equation.
3. In a chemical equation, reactants, which are the reacting substances, are given at the left side and the products, which is the result of the reactants, is given on the right side and there is an arrow pointing right in between the two. If there are more than one reactants then they are separated by a + sign.
The result should be a balanced equation, where the same number of atoms are at both sides of the equation.

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-When a substance's  appearance has changed yet  its molecular form has not changed is known as physical change. For instance water freezing, in turn becoming ice.

-When a substance's molecular form is changed either by reaction or by other means and is transformed into a new substance this process is called a chemical change. For instance a log burning.

-Referring back to the chemical change, normally a chemical reaction occurs which in simple terms is when a substance changes both chemically and physically. The atoms of the original substance is still found in the new substance, the difference is the bonds are either broken or re-bonded to form a different substance. An example of this occurrence would be a gas becoming a solid.