Presentation on theme: "Changes of Matter Physical Change- a change that alters the appearance or form of a substance but doesn’t produce a new substance. Ex: melting a sample."— Presentation transcript:
1 Changes of MatterPhysical Change- a change that alters the appearance or form of a substance but doesn’t produce a new substance.Ex: melting a sample of goldChemical Change/Reaction- a change in matter that produces one or more new substances.Ex: Gas produced from vinegar and baking soda.
2 Evidence for Chemical Reactions Gas ProductionChange in Temperature/EnergyChange in ColorChange in PropertiesFormation of a Precipitate
3 Changes in EnergyEndothermic Reactions- a reaction in which energy is absorbed. Not all endothermic reactions result in a decrease in temperature.Ex: frying an eggExothermic Reactions- a reaction in which energy is released.Ex: the burning of airplane fuel
4 Chemical FormulasA chemical formula is a combination of symbols that represents the elements present in the formula and the ratio of elements present.Ex: MgCl2 - One atom of magnesium for every two atoms of chlorine.Ratio is 1:2How many total atoms are present in the following:Pb(NO3)4 H2SO4 2HNO3
5 What Are Chemical Equations? Using formulas and symbols instead of words to represent a chemical reaction.Ex: CaCO CaO CO2Structure of an Equation*Reactants-substances you start with*Products-substances you end up with*Arrow means “yields”
6 Subscripts vs. Coefficients Subscripts – A number that indicates the ratio of elements in a compound.Ex: H2O Ratio 2:1Coefficients – a number in front of a chemical formula in an equation that indicates how many molecules or atoms of each reactant and product are involved in a reaction.Ex: 3H2O Three molecules of water
7 Conservation of MassDuring a chemical reaction, matter is not created or destroyed.Total mass of the reactants equals the total mass of the products.Open System – matter can enter from or escape to the surroundings. Ex: burning wood in a fireplaceClosed System – matter is not allowed to enter or leave.Ex: a chemical reaction in a sealed bag
8 Balancing EquationsTo describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation.Ex: 2H2O + O2 2H2O2(4 hydrogen atoms and 4 oxygen atoms are present on both sides of the equation)
10 Controlling Chemical Reactions All reactions require a certain amount of activation energy to get them started.Activation energy – the minimum amount of ofenergy needed to start a chemical reaction.
11 Factors that Influence the Rate of Reactions Surface AreaTemperatureConcentration – amount of substance in a given volumeUse a Catalyst – a material that increases the rate of a reactionUse an Inhibitor – a material that decreases the rate of a reaction