Rates Of Reaction And Energy Chnages Flashcards
(16 cards)
What is the rate of a chemical reaction?
The rate of a chemical reaction is how quickly reactants are converted into products.
Rate = Change in amount of reactant or product / Time. Units can be g/s, cm³/s, or mol/s depending on the measurement used.
What factors affect the rate of a chemical reaction?
• Concentration: Higher concentration = more frequent collisions.
• Pressure (gases): Increases particle collisions.
• Temperature: Increases energy and frequency of collisions.
• Surface Area: More exposed area = more collisions.
• Catalysts: Lower activation energy.
What is collision theory?
A reaction occurs when particles collide with sufficient energy (equal to or greater than the activation energy) and the correct orientation.
How can you measure the rate of a reaction?
• Gas syringe method: Measure volume of gas produced over time.
• Mass loss method: Track decrease in mass as gas escapes.
• Precipitation method: Time taken for a cross to disappear under cloudy solution.
How do you interpret a rate of reaction graph?
• Steeper line = faster reaction.
• Level line = reaction complete.
• Compare graphs to evaluate effects of temperature, concentration, or catalysts.
What is a reversible reaction?
A reaction that can go in both forward and backward directions.
Example: A + B <=> C + D
What is dynamic equilibrium?
In a closed system, when forward and reverse reactions occur at the same rate and concentrations of reactants and products remain constant.
What is Le Chatelier’s Principle?
When conditions change, the equilibrium position shifts to oppose the change:
• Increase in concentration: Shifts to remove added substance.
• Increase in pressure: Shifts to side with fewer gas molecules.
• Increase in temperature: Shifts to endothermic direction.
Describe the Haber Process.
• Equation: N2(g) + 3H2(g) <=> 2NH3(g) ΔH = -92 kJ/mol
• Conditions:
• Temp: 450°C
• Pressure: 200 atm
• Iron catalyst
• Compromise:
• Lower temp increases yield but slows rate.
• Higher pressure increases yield but is costly/dangerous.
• Ammonia used to make fertilisers.
• Continuous recycling of unreacted nitrogen and hydrogen.
What is an exothermic reaction?
A reaction that releases energy to the surroundings.
Examples: combustion, neutralisation. Temperature of surroundings increases.
What is an endothermic reaction?
A reaction that takes in energy from the surroundings.
Examples: photosynthesis, thermal decomposition. Temperature of surroundings decreases.
What is activation energy?
The minimum amount of energy needed for particles to react when they collide.
How is energy change shown on a reaction profile?
• Exothermic: Products lower than reactants.
• Endothermic: Products higher than reactants.
• Activation energy is shown by the peak of the curve.
• Catalysts lower the peak (activation energy).
How do you calculate energy change from bond energies?
Energy change = Bonds broken - Bonds formed.
• Breaking bonds = energy in (endothermic).
• Forming bonds = energy out (exothermic).
What is a catalyst and how does it work?
A catalyst speeds up a reaction by providing an alternative reaction pathway with lower activation energy. It is not used up.
What are the advantages of using catalysts in industry?
• Increases rate without being used up.
• Saves energy by allowing lower temperature/pressure.
• Cost-effective and reusable.
