Energetics/rates/equilibria Flashcards
What do the rates of reactions depend on?
Temperature
Concentration
Catalyst
Size of particles
Rate of reaction equation
Amount of reactant used/amount of product formed divided by time
What can be used to measure the volume of gas
Gas syringe
Advantage of using a gas syringe
Gives volumes accurate to the nearest mm
Disadvantage of using a gas syringe
If the reaction is too vigorous, you can easily blow the plunger out the end of the syringe
Why put cotton wool at the top of the conical flask in the reaction of hydrochloric acid and marble chips
Stops acid spray leaving the flask (but let’s CO2 escape)
What does a gas need to be to use an inverted measuring cylinder
Insoluble or sparingly soluble in water
Works for: oxygen, hydrogen and carbon dioxide
What does the rate of reaction depend on (collision wise)
How many successful high energy collisions there are in a given unit of time
Affect of size of particles on rate of reaction
Large particles, smaller surface area, fewer collisions, slower reaction
Smaller particles, larger surface area, more collisions, faster reaction
How can you test the affect of surface area on something
Do the experiment once with marble chops and another time with marble power
Use 5g of marble and 100cm3 of dilute Hcl in each
Why is the experiment faster with marble powder
5g of marble used in both cases so the graph levels off at the same point
The reaction is faster for the powder because there are more frequent collisions due to the greater surface area of the powder
Effect of Concentration on rate of reaction
Low concentration of solution, fewer acid particles in solution, therefore fewer collisions in the same time and slower rate
High concentration of solution, more acid particles in the same volume of solution, therefore more frequent collisions and faster rate
Effect of increasing temp on rate of reactions
Increasing temp increases the kinetic energy of the particles, the frequency of collisions increases and the proportion of high energy collisions increases
Improvement for temp experiments
Use a thermostatically controlled water bath to keep the temp constant
Exothermic reaction
Heat energy given out (small activation energy)
Endothermic reaction
Heat energy taken in (large activation energy)
What does an increase of pressure do to the rate of reactions
Increases the rate of reactions between gases but hardly affects the rate of reactions between liquids, solutions and solids (molecules/atoms/ions are already very close together)
What is a catalyst
Substance that speeds up a chemical reaction but is in unchanged in mass and is unchanged chemically during the reaction.
What does a catalyst do
Speeds up the reaction by providing an alternative reaction pathway of lower activation energy
What do catalytic converters do
Change the pollutant exhaust gases carbon monoxide and nitrogen dioxide into harmless carbon dioxide and nitrogen
What does process of making chemical bonds do
Give out energy (temp increases = exothermic)
What does process of breaking chemical bonds do
Requires energy (temp decreases = endothermic)
DeltaH negative
Exothermic
DeltaH positive
Endothermic
Reactions that result in an energy change
Combustion (always exo)
Dissolving (either)
Neutralisation (always exo)
Displacement
Sources for error in burning liquids:
Heat lost to the surroundings
Heat used to raise the temp of the flask and the thermometer
How to reduce sources of error in burning liquids
Put screen around apparatus to reduce draft
Metal + acid >
Salt + hydrogen
Heat given out =
Mass x 4.2 (specific heat capacity) x temp rise
Reversible reaction
When the products can react to form reactants
Hydrogen + nitrogen > ammonia
Forward reaction
Ammonia > hydrogen + nitrogen
Backward reaction
Dynamic
Both the forward and backward reaction are happening at the same rate
Equilibrium
Reaction has reached a point where the overall amounts of reactants and products do not change
Dynamic equilibrium
Concentration of reactants and products remain constant
When is the equilibrium on the left hand side
When there are large amounts of reactants remaining and small amounts of products present
When the equilibrium is on the right hand side
Large amounts of products have formed and very little of the reactants remain
How are reactants and products in an equilibrium affected by pressure
Increasing pressure moves the equilibrium in the direction of fewer moles of gas
Decreasing pressure moves the equilibrium in the direction of more moles of gas
How are reactants and products in an equilibrium affected by temp
Increasing temp moves the equilibrium in the endothermic direction
Decreasing temp moves the equilibrium in the endothermic direction
+ ive
Endothermic
- ive
Exothermic
Effect of catalyst on position of equilibrium and rate of reaction
Speeds up forward and reverse reactions equally so has no effect on the position of the equilibrium
