Rates of Reactions Experiment
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Questions and Answers

How can the instantaneous rate of a reaction be measured at a specific time point?

By determining the slope of the tangent to the curve at that time point on the graph.

What are the main factors that influence the rates of chemical reactions?

The nature of reactants, particle size, concentration, temperature, and catalysts.

Why do smaller particle sizes lead to faster reaction rates?

Smaller particles have a higher surface area which increases the frequency of collisions between reactants.

What must occur for a dust explosion to take place?

<p>Particles must be combustible, there must be an ignition source, the particles must be dry, and oxygen must be present.</p> Signup and view all the answers

How does increasing the concentration of reactants affect the reaction rate?

<p>Higher concentration increases the number of particles, which enhances the likelihood of collisions.</p> Signup and view all the answers

What effect does temperature have on the rate of a chemical reaction?

<p>An increase in temperature raises both the number and energy of collisions, thereby increasing the reaction rate.</p> Signup and view all the answers

What is the relationship between bond types and reaction rates?

<p>Ionic bonds generally allow for faster reactions, while covalent bonds tend to slow reactions due to bond breaking requirements.</p> Signup and view all the answers

How is the rate of reaction mathematically defined?

<p>Rate = Change in concentration (moles/L) / Time (secs).</p> Signup and view all the answers

What is meant by the rate of a chemical reaction?

<p>The rate of a chemical reaction is defined as the change in concentration per unit time of any one reactant or product.</p> Signup and view all the answers

Why do sodium chloride and silver nitrate react almost instantaneously in solution?

<p>They react almost instantaneously because both are ionic compounds that dissociate into ions in solution, allowing immediate interaction.</p> Signup and view all the answers

How can increased pressure affect the rate of reaction between hydrogen gas and nitrogen gas to form ammonia?

<p>Increased pressure results in closer molecules, leading to more collisions per unit time and a higher likelihood of effective collisions.</p> Signup and view all the answers

What effect does increasing temperature have on the reaction rate for substances like nitrogen and hydrogen gases?

<p>Increasing temperature increases the energy of molecules, resulting in more collisions that reach activation energy.</p> Signup and view all the answers

Describe how you would measure the reaction time of hydrochloric acid and sodium thiosulfate.

<p>You would place the sodium thiosulfate solution over a marked cross, add hydrochloric acid, start a stopwatch, and record the time until the cross becomes invisible.</p> Signup and view all the answers

How can you demonstrate that the rate of reaction is directly proportional to the concentration of sodium thiosulfate?

<p>By repeating the reaction with varying concentrations of sodium thiosulfate and plotting the reciprocals of the reaction times against concentration, creating a straight line.</p> Signup and view all the answers

What are the key features to include in a reaction profile diagram for an exothermic reaction?

<p>A reaction profile for an exothermic reaction should include the activation energy (EA) and the heat of reaction (∆H), indicating the energy changes during the reaction.</p> Signup and view all the answers

Why is it important to know the activation energy (EA) of a reaction?

<p>Knowing the activation energy is crucial because it helps determine the temperature conditions necessary for the reaction and its overall feasibility.</p> Signup and view all the answers

What is the purpose of swirling the flask during the experiment?

<p>The purpose of swirling the flask is to ensure that the reactants are thoroughly mixed and that the reaction proceeds uniformly.</p> Signup and view all the answers

How does temperature affect the time taken for the cross to disappear in the experiment?

<p>As the temperature increases, the time taken for the cross to disappear generally decreases, indicating a faster reaction rate.</p> Signup and view all the answers

Define a catalyst and explain its role in chemical reactions.

<p>A catalyst is a substance that alters the rate of a chemical reaction without being consumed in the process, thereby facilitating the reaction.</p> Signup and view all the answers

What distinguishes homogenous catalysis from heterogenous catalysis?

<p>Homogeneous catalysis occurs when both the reactants and the catalyst are in the same phase, while heterogeneous catalysis involves reactants and catalyst in different phases.</p> Signup and view all the answers

What happens to catalysts in the presence of catalyst poisons like lead?

<p>Catalysts can be rendered ineffective by catalyst poisons, which can bond with the catalyst and inhibit its catalytic activity.</p> Signup and view all the answers

Why is it important to record the temperature in the experiment on thiosulfate and hydrochloric acid?

<p>Recording the temperature is crucial because it directly impacts the rate of the reaction and allows for accurate analysis of the effects of temperature.</p> Signup and view all the answers

What does the graph of 1/time against temperature indicate in the context of reaction rates?

<p>The graph of 1/time against temperature indicates the relationship between temperature and reaction rate, where a steeper slope suggests a higher rate of reaction at elevated temperatures.</p> Signup and view all the answers

How do catalysts help achieve equilibrium in chemical reactions?

<p>Catalysts help achieve equilibrium more quickly by speeding up both the forward and reverse reactions equally.</p> Signup and view all the answers

What is autocatalysis and how does it affect a chemical reaction?

<p>Autocatalysis is when one of the products of a reaction acts as a catalyst for that reaction, accelerating its progress.</p> Signup and view all the answers

Describe the Intermediate Formation Theory in the context of catalysis.

<p>The Intermediate Formation Theory states that a catalyst forms an intermediate compound during a reaction, such as the formation of the IO- intermediate when hydrogen peroxide is decomposed by I- ions.</p> Signup and view all the answers

Explain the Surface Adsorption Theory and its significance in heterogeneous catalysis.

<p>The Surface Adsorption Theory indicates that reactant molecules accumulate at the surface of a catalyst, where reactions occur due to higher concentration and bond formations.</p> Signup and view all the answers

What materials are commonly used as catalysts in catalytic converters?

<p>Catalytic converters commonly use Platinum, Palladium, and Rhodium as catalysts to convert pollutants into less harmful substances.</p> Signup and view all the answers

What happens in the desorption stage of a catalytic reaction?

<p>In the desorption stage, the products of the reaction leave the surface of the catalyst, allowing more reactants to be adsorbed and continue the reaction cycle.</p> Signup and view all the answers

What is the role of a catalytic converter in environmental protection?

<p>It converts harmful gases like carbon monoxide and nitrogen monoxide into less harmful substances, such as carbon dioxide and nitrogen.</p> Signup and view all the answers

Why are lead and sulfur considered catalyst poisons?

<p>They form permanent bonds on the catalyst surface, preventing effective collisions and inactivating the catalyst.</p> Signup and view all the answers

What is an effective collision in the context of chemical reactions?

<p>An effective collision is one that occurs with sufficient energy to break existing bonds and form new products.</p> Signup and view all the answers

Define activation energy in chemical reactions.

<p>Activation energy is the minimum energy required for colliding particles to react and form products.</p> Signup and view all the answers

How does the poisoning of catalysts affect catalytic converters?

<p>It reduces the converter's efficiency by preventing the necessary reactions from occurring.</p> Signup and view all the answers

What toxic effect does nitrogen monoxide have on the environment?

<p>Nitrogen monoxide contributes to acid rain and is poisonous, affecting both health and ecosystems.</p> Signup and view all the answers

What environmental problems do hydrocarbons cause?

<p>Hydrocarbons contribute to smog formation and the greenhouse effect.</p> Signup and view all the answers

What happens during a collision between reacting particles for a reaction to occur?

<p>The particles must collide with enough energy to break bonds, leading to the formation of new bonds and products.</p> Signup and view all the answers

What is the purpose of a reaction profile diagram?

<p>It shows the change in energy of a chemical reaction with time as the reaction progresses.</p> Signup and view all the answers

How does a catalyst affect the activation energy of a reaction?

<p>A catalyst reduces the activation energy required for a reaction to occur.</p> Signup and view all the answers

Explain how the formation of sulfur is observed during the reaction.

<p>A precipitate of sulfur is formed, causing the solution to turn cloudy.</p> Signup and view all the answers

Describe the method used to determine reaction times in the experiment.

<p>The flask is placed over a marked cross and the time is recorded when the cross becomes invisible.</p> Signup and view all the answers

What kind of relationship exists between temperature and the rate of reaction based on the experiment?

<p>The rate of reaction increases exponentially with temperature.</p> Signup and view all the answers

How would changing the concentration of sodium thiosulfate to 0.025 M affect the reaction time?

<p>The reaction time would increase compared to using 0.05 M sodium thiosulfate.</p> Signup and view all the answers

What does the graph of reaction rate versus temperature reveal about reaction dynamics?

<p>It shows a positive correlation between temperature and reaction rate.</p> Signup and view all the answers

At 35 ºC, what is the calculated reaction time based on the graph?

<p>The reaction time is approximately 69 seconds.</p> Signup and view all the answers

Study Notes

Rates of Reactions

  • Chemists use the term "rate of reaction" to describe how quickly chemical changes occur.
  • The rate of reaction is defined as the change in concentration per unit time of any one reactant or product.

Mandatory Experiment: Monitoring the Rate of Oxygen Production from Hydrogen Peroxide

  • Procedure:

    • Measure 5cm³ of hydrogen peroxide and dilute to 50cm³ with water, placing it in a conical flask.
    • Weigh 0.5g of manganese(IV) oxide and suspend it in the conical flask using a thread and stopper, avoiding direct contact with the peroxide.
    • Fill a graduated cylinder with water and invert it over a beehive shelf.
    • Inject air into the graduated cylinder until the water level is at the 10cm³ mark.
    • Arrange a delivery tube to collect the produced oxygen in the graduated cylinder.
    • Loosen the stopper momentarily to allow the thread to fall and shake vigorously to mix the manganese(IV) oxide with the hydrogen peroxide.
    • Start the stop-clock when contact is made.
    • Record the total volume of gas in the graduated cylinder every 30 seconds.
    • Record readings at eye level.
    • Draw a graph of total volume of oxygen against time, with time on the horizontal axis.

  • Definition: Instantaneous rate of reaction is the rate of reaction at any one particular time during the reaction.

Factors Affecting Rates of Reactions

  • Nature of Reactants:

    • Rates depend on the bonds involved. Ionic bonds react faster than covalent bonds (where bonds need to be broken before a reaction occurs).
    • Smaller particle size leads to faster reactions due to higher surface area.
    • Powdered chemicals react faster than large pieces of the same substance.

  • Concentration: Higher concentration of reactants leads to a faster reaction rate because more particles mean more chances of collision.

  • Temperature: Increased temperature increases the number of collisions and the amount of energy in each collision, leading to a faster reaction rate.

  • Catalysts:

    • Catalysts are substances that alter reaction rates without being consumed in the process.
    • They are specific, needing very small amounts to function.
    • Catalysts are involved in many industrial processes and everyday chemical reactions.

  • Temperature:

    • Increasing the temperature increases the rate of a reaction.
    • It increases the number of collisions and the amount of energy in each collision.

Mandatory Experiment: Concentration and Rate

  • Procedure:
    • Use 100cm³ of Na₂S₂O₃ solution in a conical flask.
    • Add 10cm³ of 3M HCl, starting a stop clock simultaneously.
    • Swirl the flask with cross on a piece of white paper.
      • Record the time taken for the cross to disappear
    • Repeat the experiment with varying amounts of Na₂S₂O₃ solution (80cm³, 60cm³, 40cm³, and 20cm³), always making the total volume 100cm³ with water.
    • The initial concentration of Na₂S₂O₃ should be 0.1M, with subsequent concentrations of 0.08M, 0.06M, 0.04M, and 0.02M, respectively.
    • Record the results.
  • Graph: Plot a graph of 1/time vs concentration.

Mandatory Experiment: Effect of Temperature on Reaction Rate

  • Procedure:

    • Place 100 cm³ of 0.05M Na₂S₂O₃ solution into a conical flask.
    • Warm the flask until the temperature is around 20°C.
    • Add 5cm³ of 3M HCl, starting the stop-clock.
    • Record the exact temperature.
    • Time how long it takes for the cross to disappear
    • Repeat using different temperatures (approx. 30°C, 40°C, 50°C, and 60°C).

  • Graph: Plot 1/time vs. Temperature.

    • Describe the relationship on the graph between rate of reaction and temperatures

Catalysts

  • Definition: A catalyst alters the rate of a chemical reaction without being consumed.
  • General Properties: Catalysts participate in reactions but are recovered unchanged. They are specific to the type of reaction they catalyse. Increased catalyst amount does not significantly change reaction rate, only needing small amounts to function.
  • Types:
    • Homogenous: Reactants and catalyst in the same phase. Example: iodine clock experiment.
    • Heterogeneous: Reactants and catalyst in different phases, having a boundary. Example: Methanol to Methanal oxidation using a red-hot platinum wire catalyst.
    • Autocatalysis: One of the products acts as a catalyst. Example: peroxide catalysis.
  • Mechanisms:
    • Intermediate formation theory: Catalysts form intermediates.
    • Surface adsorption theory: Substances accumulate on the catalyst’s surface, where reactions occur.

Collision Theory and Activation Energy

  • Effective collision: A collision with enough energy to form products.
  • Activation energy: Minimum energy colliding particles need for effective collision.
  • Activation energy is affected by catalysts.

Reaction Profile Diagrams

  • Graphs illustrating energy changes in chemical reaction over time
  • Activation energy: Minimum energy required for a reaction to proceed.
  • Exothermic reactions: Release heat; products have lower energy than reactants.
  • Endothermic reactions: Absorb heat; products have higher energy than reactants.

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Rates Of Reactions PDF - Educational Chemistry Past Paper

Description

Explore the process of measuring the rate of reaction through a practical experiment involving hydrogen peroxide and manganese(IV) oxide. This quiz covers the steps and scientific principles behind observing oxygen production. Test your knowledge on reaction rates and key experimental techniques.

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