chemical reaction

when chemical reactions occur

occur when 1+ new substances are formed. during a chemical reaction:

- atoms in the reactants r rearranged

- some chemical bonds r broken

- new chemical bonds form

- new substances r produced

sign of a chemical reaction

change in colour/temperature, production of light/sound, disappearance of a solid, formation of a new solid, formation of gas (shown by fizzing or a new odour)

physical changes

Rule: Do not produce new substances.

Particles: Same particles remain, but their position, arrangement, movement, or state may change.

Why are changes of state considered physical changes?

Substance remains chemically the same.

chemical changes

produce at least one new substance. the atoms r rearranged and new chemical bonds form

reactants

substances present at the start of a chemical equation, written on the left-hand side

products

new substances formed by the reaction, written on the right hand side.

What happens over time as a reaction proceeds?

Reactants Decrease over time.

Products Increase over time.

Monitoring Measured by checking reactant or product amounts at different times.

how does temperature affect reaction rate

The Effect: Higher/lower temperature speeds up or slows down the rate products form.

Core Rule: Changes the rate only—does not change the fundamental identity of the products.

state symbols

(s) Solid, (l) Liquid, (g) Gas, (aq) Aqueous (dissolved in water)

composition reactions

occur when 2+ reactants combine to form a product (general pattern: A+B→AB; many substances → one combined substance)

decomposition reactions

occur when 1 reactant breaks down into 2+ more products (general pattern: AB→A+B; one substance → multiple simpler substances)

law of conservation of mass

mass is neither created nor destroyed during a chemical reaction. therefore, mass of reactants = mass of products

conservation of atoms

because atoms r conserved, there must be the same number of each type of atom on both sides