Topic 7 - Rates of Reaction and Energy Changes Flashcards
2 ways of investigating the rate of reaction
Measuring the production of gas by change in mass or measuring volume of gas given off
Observing a colour change
How to investigate rate of reaction by observing a colour change
When two colourless solutions are used that produce a precipitate
The precipitate clouds the solution and the mark underneath disappears
How fast it disappears shows rate of reaction
How to investigate rate of reaction by measuring gas produced
Let gas straight out of beaker on mass balance and observe the speed that the mass drops
Or
Connect beaker to gas syringe to measure how fast the volume of gas increases
Rate of reaction=
Amount of product formed / Time
Surface area on Rate of reaction core practical
Use Dilute HCl and marble chips with a gas syringe attached to the beaker. Repeat with smaller marble chips and observe the change in rate
Temperature on rate of reaction core practical
Sodium thiosulfate and hydrochloric acid mixed in beaker with a mark underneath. A yellow precipitate should form. Use a water bath to heat up the substances before mixing. Change the temperature of water bath and observe difference in rate
The collision theory states
The collision frequency of reacting particles affects the rate of reaction.
The particles need a minimum amount of energy to react called the activation energy
The more collisions,
The higher the rate of reaction
Collision frequency is affected by
Temperature, concentration/pressure, higher surface area of solid particles
How to interpret rate of reaction from a volume/mass to time graph
The gradient of the line, or the tangent at a point on a curved graph
What do catalysts do
Increase rate of reaction without being chemically changed or used up
How do catalysts increase rate
Decreasing the activation energy
Enzymes are
Biological catalysts that speed up reactions in living cells
Enzymes are used in making
Alcoholic drinks by catalysing reaction of converting sugars to ethanol and CO2
4 types of reaction when there are changes in heat energy
Salts dissolving in water
Neutralisation
Displacement
Precipitation
Heat energy changes in dissolving salts in water
Can be endothermic or exothermic
Heat energy changes in neutralisation reactions
Mostly exothermic
Heat energy changes in displacement reaction
Exothermic
Heat energy changes in displacement reactions
Exothermic
An exothermic reaction is one where
Energy is given out to the surrounding, usually in the form of heat. Shows an increase in surrounding temp.
An endothermic reaction is one where
Energy is taken in from the surroundings, usually in the form of heat. Usually shown in a decrease in surrounding temperature
Activation energy is
The minimum amount of energy needed for bonds to break
Bond breaking is
Endothermic
Bond formation is
Exothermic
Bonds in endothermic reactions
The energy used to break bonds is greater than energy released by forming bonds
Bonds in exothermic reactions
The energy released by bond formation is greater than the energy used to break bonds
Overall energy change during a reaction =
Energy used to break bonds - Energy released by forming bonds
Positive and negative overall energy change means
Positive - Endothermic
Negative - Exothermic
Endothermic reaction profile features
Activation energy is big
Energy is absorbed so the products stay high in energy
Products above reactants in energy
Exothermic reaction profile features
Small activation energy
Energy is released so the products are low in energy
Reactants are above products in energy
