C8

The reaction mixture is connected to a gas syringe or an upside-down measuring cylinder to collect gas produced during the reaction.
The rate of reaction is calculated as:
Rate = Volume of gas produced / Time taken
Volume is measured in cm³ and time in seconds, therefore the unit for rate is cm³/s.
Diagram Components:
- Reaction mixture
- Gas syringe
- Rubber tubing

To find the rate at a specific time, draw a tangent to the graph representing the reaction progress and calculate its gradient.
Example:
- At 50s, the mass loss = 0.70g
- At 100s, mass loss = 0.007g/s
- Gradient is calculated as the change in y (mass) divided by the change in x (time), forming a right-angled triangle from the tangent.

The rate of a reaction indicates how quickly reactants are converted to products.
Rate can be measured by:
- Using up a reactant:
  - Mean rate = Quantity of reactant used / Time taken
- Producing a product:
  - Mean rate = Quantity of product formed / Time taken
For gas reactions, measure changes in mass or volume.

Example Calculation:
- Mass at 100 seconds: 0.80g
- Mass at 50 seconds: 0.56g
- Change in mass = 0.80g - 0.56g = 0.24g
- Change in time = 100s - 50s = 50s
- Mean rate of reaction = 0.24g / 50s = 4.8 x 10⁻³ g/s

Steep gradients indicate high reaction rates, while shallow gradients indicate slower rates.
For a reaction to proceed, particles must collide with sufficient energy, termed activation energy.
Rate can be increased by:
- Increasing the frequency of collisions.
- Increasing particle energy during collisions.

Catalysts are substances added to increase the reaction rate that are not consumed in the reaction.
They provide an alternate pathway for the reaction with lower activation energy, enhancing the probability of successful collisions.

Increasing Temperature
- Method: Heat the container.
- Effect: Particles move faster, leading to more frequent collisions and reactions due to higher energy.
Increasing Concentration of Solutions
- Method: Use a more concentrated solution.
- Effect: More reactant particles lead to more frequent collisions.
Increasing Pressure of Gases
- Method: Increase gas quantity or reduce container size.
- Effect: Closer particle proximity results in more collisions.
Increasing Surface Area of Solids
- Method: Cut solids into smaller pieces or grind into powder.
- Effect: More surface area leads to more exposed particles for reaction.

The reaction mixture is placed on a mass balance to measure mass loss as gas is released.
Rate is defined by:Rate = Change in mass / Time taken
Mass is measured in grams, and time in seconds; unit for rate is g/s.

External conditions affecting a reaction include:
- Concentration of reactants.
- Temperature of the reaction vessel.
- Pressure inside the vessel.

Increasing Pressure: Favors reactions yielding fewer gas molecules, countering the increase in pressure.
Decreasing Pressure: Favors reactions yielding more gas molecules.

At equilibrium, amounts of reactants and products remain constant.
To alter the amounts at equilibrium, change the reaction conditions, prompting a shift toward either the forward or reverse reaction.
Example: Lowering product concentration favors the forward reaction to restore the product amount.

In a closed system, reactants and products cannot escape, leading to eventual dynamic equilibrium.
At this point:
- Reactants convert to products and vice versa.
- Rates of both processes are equal, keeping overall amounts constant.

Products can revert to reactants in reversible reactions, denoted with the symbol \u2194.
Energy changes differ based on the direction of the reaction, where endothermic and exothermic processes correspond oppositely.

Answers to key questions regarding rates of reactions and equilibrium conditions must be written down and tested for retention by covering answers.