Rates of Reactions, Energy Changes and Equilibrium Flashcards
Rate of reaction definition
How quickly a reaction happens
Rate of reaction formula
Amount of reactant used or amount of product formed / time
Methods of measuring rate of reaction
Precipitation
Change of mass
Volume of gas given off
Precipitation method
Works on two see-through solutions that will produce a precipitate
Mix two solutions in a flask over a piece of paper with mark on it
Observe and measure how long mark disappears
Subjective as different people may disagree when mark disappears
Change in mass (measuring rate of reaction) method
Works on any reaction that produced a gas
Measure mass of reactants on mass balance
Measure time taken for reaction to finish (when mass balance stops changing)
Measure amount of gas lost and compare with time
Volume of gas (measuring rate of reaction) method
Press gas syringe to smallest it can get
Attach it to flask with reactants
More gas given off = faster reaction
Reaction is over when no more gas produced
Have to use right size or else syringe plunger will blow out
Factors affecting rate of reaction
Collision frequency (temperature, concentration, surface area) Energy transferred (temperature, catalyst)
Catalyst definition
Substance that increases rate of reaction without being used up
Catalyst facts
Provides alternative reaction pathway with lower activation energy
Decreases minimum activation energy
Very fussy with which reactions they can catalyse
Enzyme definition
Biological catalysts
Exothermic reaction definition
Reaction that gives out more energy to the surroundings than taking in energy, making it warmer
Endothermic reaction definition
Reaction that takes in more energy from surroundings than giving energy out, making it cooler
Exothermic reaction on reaction profile
Energy in reactants is higher than in products
Difference in height is amount of energy given out
Endothermic reaction on reaction profile
Energy in reactants is lower than in products
Difference in height is amount of energy from surroundings absorbed
Activation energy definition
Minimum amount of energy needed for bonds to break and a reaction to start
Difference in height between reactants and highest point on curve
Measuring temperature change method
Put polystyrene cup into large beaker of cotton wool
Add known volume of first reagent into cup
Measure initial temperature of solution
Add second reaction and stir the reaction mixture
Put lid to reduce energy lost through evaporation
Record maximum or minimum temperature
Calculate temperature
Temperature changes in reactions
Dissolving ammonium chloride = endo Calcium chloride = exo Most neutralisation = exo Ethanoic acid + sodium carbonate = endo Displacement reaction = exo Precipitation reaction = exo
BendoMex
Breaking bonds = endothermic
Making bonds = exothermic
Overall energy change formula
Energy required to break bonds - energy released to form bonds
Reversible reaction definition
When products of a reaction can react with each other to form the original reactions
Haber Process
Process to make ammonia
N2 + 3H2 <==> 2NH3
Carried out at 450°C, 200 atmospheres and iron catalyst
How reversible reactions work
As reactants react, their concentration decreases so the rate of forward reaction goes down
The concentration of products then increases so the rate of backward reaction increases
Eventually rate of forward and backward reactions are equal (equilibrium)
Things that change position of equilibrium
Temperature
Pressure
Concentration
Le Chatelier’s Principle
If there is a change in temperature, pressure or concentration in s reversible reaction, the equilibrium position will change to counteract the change
