Higher
Answer
Flashcards · 8462 · Topic 6
The rate and extent of chemical change flashcards
12 cards on Topic 6. Pick a subtopic or study them all.
Study mode needs JavaScript. Every card is listed below, so you can still cover the answers and test yourself.
Choose your cards
Session complete
Worth another look:
All 12 cards
For a quick read-through or printing. Cover the right-hand side to test yourself. Cards marked Higher are Higher tier content only.
Topic 6: The rate and extent of chemical change
- Mean rate of reaction: formula and units
- Quantity of reactant used (or product formed) ÷ time taken. Units g/s or cm³/s. Example: 84 cm³ in 60 s → 1.4 cm³/s.
- 0.44 g of CO₂ (Mr 44) forms in 50 s. Mean rate in mol/s?Higher
- 0.44 ÷ 44 = 0.010 mol; 0.010 ÷ 50 = 2.0 × 10⁻⁴ mol/s
- How do you find the rate at one moment from a graph?Higher
- Draw a tangent to the curve at that time and find its gradient: (y₂ − y₁) ÷ (x₂ − x₁), using two points far apart on the tangent.
- The five factors that increase the rate of reaction
- Higher concentration, higher pressure (gases), larger surface area (smaller pieces), higher temperature, and adding a catalyst.
- Use collision theory to explain why a higher temperature increases the rate
- Particles move faster, so collisions are more frequent and more energetic: more collisions have at least the activation energy, so more are successful.
- How does a catalyst increase the rate?
- It provides a different reaction pathway with a lower activation energy. It is not used up and is not written in the equation.
- Required practical 5: the disappearing cross method
- Put a flask of sodium thiosulfate solution on a paper cross, add hydrochloric acid and start the timer; stop it when the cross disappears. Relative rate = 1 ÷ time. Repeat for other concentrations.
- Reversible reactions and energy
- The products can react to produce the original reactants (⇌). If one direction is exothermic, the other is endothermic, and the same amount of energy is transferred.
- Equilibrium
- In a closed system, when the forward and reverse reactions occur at exactly the same rate. The reactions do not stop.
- Le Chatelier's PrincipleHigher
- If a condition is changed at equilibrium, the system responds to counteract the change.
- Effect of raising the temperature on an equilibriumHigher
- The equilibrium shifts in the endothermic direction. If the forward reaction is exothermic, the relative amount of products decreases.
- 2NO₂(g) ⇌ N₂O₄(g). Effect of increasing the pressure?Higher
- Shifts to the side with fewer gas molecules: to the right, towards N₂O₄ (1 molecule instead of 2).