4.1 Rates of Reactions Flashcards
Activation Energy
The required energy that particles need to react, if particles don’t have this energy, they will just rebound and remain unchanged
Collision Frequency
How often do particles collide with each other?
Percentage success
What percentage of the collisions have enough energy?
Factors effecting rate of reaction
- Surface Area
- Temperature
- Catalysts
- Concentration/Pressure
Surface area, Rate
- Increasing surface area increases rate of reaction
- As more of the solid is exposed to particles
- Meaning the collision frequency is higher
- So there are more successful collisions per unit time
Concentration/Pressure, Rate
- Higher solution concentration/gas pressure increases rate of reaction
- As there are more particles per unit volume
- Meaning collision frequency is higher
- Meaning more successful collisions per unit time
Temperature, Rate
- Increase temperature increases rate of reaction
- As the particles have more kinetic energy
- Meaning the percentage of collisions with enough energy is higher
- Meaning more successful collisions per unit time
Catalysts, Rate
- Presence of a catalyst increase rate of reaction
- As they provide an alternate route with a lower activation energy
- So the percentage of collisions with enough activation energy is higher
- Meaning more successful collisions per unit time
How do you increase surface area?
Cut or grind up solid, smaller prices = higher surface area
Marble Chip Experiment
- The effect of surface area on rate is usually measured by reacting calcium carbonate chips and hydrochloric acid
- Higher surface area = more gas produced in 10s (not overall)
- Gas Syringe
Equation for Marble Chip Experiment
CaCO3 (s) + 2HCl —> CaCl2(aq) + H2O(l) + CO2(g)
Marble Chip Experiment Variables
Input: Different sizes of chips
Output: Amount of gas produced
Controls: Temp, Mass of CaCO3, Volume and Conc of HCl
Marble Chip Experiment Graph
- Higher Surface Area = Steeper line
- Same final volume as amount of reactants has not changed
Rate of Reaction Equation
Rate = Change in reactant or product/time taken
Disappearing across Experiment
- The effect of concentration is usually demonstrated by reacting sodium thiosulphate solution with Hydrochloric Acid
- Sulphur is slowly produced and you can’t see through mixture after a while
Equation for disappearing cross experiment
Na2S2O3 + 2HCl —> 2NaCl + S + SO2 + H2O
Disappearing Cross Experiment Variables
Input: Concentration is Sodium Thiosulphate
Output: time taken for cross to disappear
Controls: Total volume, Concentration of HCl, Temp
rate = 1/time
Disappearing Cross Experiment Results
- Graph shows a straight line, meaning it’s directly proportional
- Meaning double concentration, doubles rate of reaction
Magnesium and Acid Experiment
- This experiment is used to show the effect of temperature by reacting magnesium and hydrochloric acid
- Heat HCl until magnesium dissapears
Magnesium and Acid Experiment Equation
Mg + 2HCl —> MgCl2 + H2
Magnesium and Acid Experiment Variables
Input: Temp of HCl
Output: Time taken for Mg to disappear
Controls: Mass & SA of magnesium, Volume and conc of HCl
Magnesium and Acid Experiment Results
- Not directly proportional, not a straight line
- Doesn’t go through origin because rate isn’t 0 and 0 degrees
What are catalysts?
- Increase Rate
- Remain Chemically Unchanged
How do catalysts work?
-Provide an alternate route with lower activation energy
Hydrogen Peroxide Experiment
- Shows the effect of catalysts using the decomposition of hydrogen peroxide
- The reaction is normally very slow but is catalysed by manganese oxide
- Use different catalysts
Hydrogen Peroxide Experiment Equation
2H2O2 —> 2H2O + O2
-The catalyst is not in the equation as it’s unchanged
Colour of manganese oxide
Black Solid
Hydrogen Peroxide Experiment Variables
Input: Which catalyst is used
Output: Volume of O2
Controls: Temp, Mass and SA of mg, Conc and Vol of H2O2
Hydrogen Peroxide Experiment Results
- More effective catalysts increase rate more effectively (steeper line)
- All lines flatten out eventually
Disappearing Cross
Used to show when a material is formed and makes liquid opaque
Gas Syringe
Measures amount of gas produced, very accurate and easy to read, gas could leak or move too quickly
Mass lost
Measures how much mass has left the conical flask (gas), easy to set up, could lose gas before timer starts
Collecting gas underwater
Measures amount of gas produced, can get easy readings, gas may dissolve or leak, hard to read
