Topic 10 - Rates Of Reaction Flashcards
(39 cards)
Activation energy
The energy needed to start a reaction.
Exothermic reaction
Transfers heat energy to the surrounding so the temperature of the surroundings increases.
Endothermic reaction
Absorbs heat energy from the surroundings so the temperature of the surroundings decreases.
Breaking bonds
Endothermic
Making bonds
Exothermic
Acronym to remember breaking bonds and making bonds?
Bendomex
Energy profile diagram:
Exothermic reaction
Overall, more heat energy is released in the making of bonds in the reactants, than is needed to break the bonds in the reactants.
Energy profile diagram:
Endothermic reaction
More heat energy is needed in the breaking of bonds in the reactants than is released in the making of the bonds on the reactants.
Bond energies
Total energy change = Total energy in - Total energy out
What is needed for a reaction to occur?
• For a reaction to occur particles need to collide.
• The particles can be a molecule, ion or atoms.
• The particles need to collide with enough energy for particles to reaction - the activation energy is the minimum energy needed.
Effective collision/Successful collision
Collisions between atoms or molecules that successfully transfer enough energy for the atoms or molecules to react together.
Four way in which a reaction can be increased?
The collision model helps explain this.
1) Increasing the temperature.
2) Increasing the surface area.
3) Increasing the concentration in a reacting solution.
4) Increasing the pressure in a reacting gas.
Concentration
• Increases the number of reactant particles in the same volume.
• Therefore collision occur more often
• Therefore rate increases.
Temperature
• The higher the temperature, the faster the particles move.
• Therefore, particles will collide more frequently.
• And with more energy meaning more successful collisions
• Therefore rate increases.
Surface area
• The greater the surface area, the more particles there are on the surface where collisions happen.
• Therefore, there will be more collisions per second.
• Therefore rate increases.
Mean rate of reaction
A measure of how quickly a reacting is used up, or a product is formed.
Quantity of reaction used / Time
OR
Quantity of product formed / Time
How to calculate rate of reaction at a certain time?
Draw a tangent on the curve at the specified time and use this equation to calculate the gradient.
Catalysts
A substance that speeds up the rate of a reaction without altering the products of the reaction, being itself unchanged chemically and in mass at the end of the reaction.
How do catalysts reduce costs in industrial processes?
• By making products more quickly.
• By allowing reactions to occur at lower temperatures.
• Catalysts do not usually need to be replaced because they are not used up.
How does a catalyst increase the rate of reaction?
• A catalyst provides an alternative reaction route, which requires less activation energy.
• The catalyst does not alter the overall energy change.
• As less activation energy is needed to start the reaction, more reactant molecules have enough energy and so more collisions are successful.
What are enzymes?
Large complex protein molecules that act as catalysts in biological reactions.
How are enzymes used in the production of alcoholic drinks?
• Alcoholic drinks are produced using an enzyme in yeast.
• This enzyme catalyses the reaction in which glucose is converted into ethanol (alcohol) and carbon dioxide.
Core practical:
Rates of reaction with syringe
1) Set up gas collection apparatus. Clamp the syringe in place.
2) 50cm3 2M Hydrochloric Acid.
3) 5g of marble chips.
4) QUICKLY place bung into conical flask AND start the timer.
5) Measure and record volume on gas syringe every 10 s, for 100s.
6) Decant out any excess liquid, discard any solid and rinse.
7) Repeat the experiment with different sized marble chips or different concentration of acid.
Core practical:
Rates of reaction with syringe
Word equation and balanced equation
Calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)