chemical reactions

y9 t1 science exam

rate of reaction

how fast a chemical reaction happens

how to measure rate of reaction

change in mass (gas escaping), volume of gas, change in colour or concentration, change in pH

what does chemical reaction look like on a graph

steeper gradient = faster reaction

collision theory condition 1: sufficient energy

colliding particles must have at least the activation energy - minimum energy needed to break bonds and start reaction

collision theory condition 2: correct orientation

particles must hit eachother at the right angle for bonds to break and reform correctly

4 factors that change reaction rate

temperature, concentration, surface area, catalyst

reaction rate factor 1: temperature

higher temperature means particles move faster. collisions have more energy, which is more overcome activation energy

10 degrees celcius increase

reaction rate approximately doubles

reaction rate factor 2: concentration

higher concentration means more particles in the same volume. collides more often

reaction rate factor 3: surface area

smaller particles means greater surface area exposed. more surface particles available to collide

reaction rate factor 4: catalyst

provides a alternative reaction pathway which has a lower activation rate because more particles have enough energy to collide.

what happens to catalyst

Not consumed and regenerated at the end. It does not appear in final chemical equation

exothermic reactions

releases energy to surroundings and is hot. H= negative

exothermic chemical energy

more chemical energy in reactants than products

endothermic reaction

Absorb heat from surroundings and is cold. H = positive

endothermic chemical energy

Products have more chemical energy than reactants

valence electrons

control how atoms behave in chemical reactions. Gain, lose or share valence electrons during reaction

chemical reactions

forms new substances from starting substances called reactants. Reactants change into products because atoms rearrange into different combinations

conservation of atoms

atoms are rearranged; they are not created or destroyed in chemical reactions. Total mass remains the same

bonding shift

old bonds break and new bonds form to create products

observational evidence

Includes colour change, gas formation, temperature change, precipitates and light release. Not all reactions show every type of evidence at a time

evidence 1: colour change

suggests new substance formed due to different colour composition. Colour changes permanently

evidence 2: gas production

shows bubbles forming indicating gaseous substance

evidence 3: temperature change

indicates energy transfer during atomic bond breaking and forming

evidence 4: precipitate formation

forms when a solid appears from mixing two liquid solutions together

evidence 5: light and sound

rapid energy changes indicate chemical reaction taking place intensely

reactant

starting solution (left side of equation)

product

new substances formed (right side of equation)

Format of word equation

Reactant + Reactant (arrow) product