Rates of Reactions Lab Experiment
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Questions and Answers

What does the leveling off of the curve in the graph indicate about the reaction over time?

  • The reaction is accelerating.
  • The reaction is nearing completion. (correct)
  • The reaction is becoming more exothermic.
  • The reaction speed is constant.

How is the instantaneous rate of reaction at 2 minutes calculated?

  • By drawing a vertical line at 2 minutes.
  • By measuring the area under the curve.
  • By calculating the average rate from 0 to 2 minutes.
  • By finding the slope of the tangent to the curve at that point. (correct)

Which factor is NOT mentioned as affecting reaction rates?

  • Pressure (correct)
  • Nature of reactants
  • Concentration
  • Temperature

What is the effect of smaller particle size on reaction rates?

<p>It speeds up reactions due to a higher surface area. (B)</p> Signup and view all the answers

Which type of bonds generally leads to faster reactions?

<p>Ionic bonds (A)</p> Signup and view all the answers

What is a potential hazard of using finely divided particles in reactions?

<p>They can cause a dust explosion. (D)</p> Signup and view all the answers

What does the slope of a tangent line represent in the context of reaction rates?

<p>The instantaneous rate of reaction. (A)</p> Signup and view all the answers

Why do powdered chemicals tend to react more quickly than larger pieces?

<p>They provide a larger surface area for collisions. (B)</p> Signup and view all the answers

What is the correct definition of the rate of a chemical reaction?

<p>The change in concentration per unit time of any one reactant or product. (C)</p> Signup and view all the answers

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

<p>They are ionic compounds that dissociate fully in solution. (C)</p> Signup and view all the answers

How does increasing the pressure affect the rate of reaction between hydrogen gas and nitrogen gas?

<p>It promotes more collisions per unit time. (A)</p> Signup and view all the answers

What would you observe if you plotted the reciprocals of the times against the concentrations of sodium thiosulfate?

<p>A straight line through the origin. (B)</p> Signup and view all the answers

In an exothermic reaction, what does the activation energy (EA) represent?

<p>The energy required to initiate the reaction. (B)</p> Signup and view all the answers

What is the role of catalysts in a catalytic converter?

<p>To facilitate reactions without being consumed (A)</p> Signup and view all the answers

Which condition is NOT needed for a dust explosion to occur?

<p>Particles must be wet (B)</p> Signup and view all the answers

What happens during the desorption stage of the catalytic conversion process?

<p>Products leave the catalyst surface (C)</p> Signup and view all the answers

Which of the following is a common catalyst poison?

<p>Lead (D)</p> Signup and view all the answers

What effect does an increase in the concentration of reactants have on the rate of reaction?

<p>Increases the rate of reaction (D)</p> Signup and view all the answers

What is required for a collision between particles to be effective?

<p>The particles must collide with a minimum energy (D)</p> Signup and view all the answers

What is the correct relationship between temperature and the rate of reaction?

<p>Higher temperature increases the rate of reaction (B)</p> Signup and view all the answers

Which product results from the reaction of carbon monoxide in a catalytic converter?

<p>Carbon dioxide (D)</p> Signup and view all the answers

If the initial concentration of sodium thiosulfate is 0.1 M, what is the concentration after diluting it to 60 cm³ with water?

<p>0.06 M (D)</p> Signup and view all the answers

Why do catalytic converters need to be changed after approximately 80,000 Km?

<p>The catalysts are poisoned (D)</p> Signup and view all the answers

What is the method to calculate the rate of reaction from the time taken for the cross to disappear?

<p>Rate = 1 / Time (D)</p> Signup and view all the answers

What is the expected conclusion from a graph plotting reaction rate (1/t) against concentration of sodium thiosulfate?

<p>Reaction rate increases as concentration increases (C)</p> Signup and view all the answers

What is an effective collision?

<p>A collision that results in the formation of products (C)</p> Signup and view all the answers

What role do the precious metals like Platinum and Palladium play in a catalytic converter?

<p>They serve as catalysts for chemical reactions (C)</p> Signup and view all the answers

Which of the following steps is NOT part of the mandatory experiment with sodium thiosulfate and hydrochloric acid?

<p>Measure the temperature of the reaction mixture (B)</p> Signup and view all the answers

What happens when sodium thiosulfate concentration is decreased during the experiment?

<p>Rate of reaction slows down (A)</p> Signup and view all the answers

What is the primary role of a catalyst in a chemical reaction?

<p>To increase the rate at which equilibrium is achieved (D)</p> Signup and view all the answers

What defines heterogenous catalysis?

<p>The catalyst is in a different phase from the reactants (C)</p> Signup and view all the answers

In the example of the iodine snake experiment, which component acts as the catalyst?

<p>Potassium iodide (C)</p> Signup and view all the answers

What occurs during autocatalysis?

<p>One of the products catalyzes the reaction (A)</p> Signup and view all the answers

How does a catalyst accelerate a reaction through the intermediate formation theory?

<p>By forming an intermediate compound during the reaction (D)</p> Signup and view all the answers

What is a common issue that can arise with catalysts, such as in catalytic converters?

<p>They can be rendered ineffective by catalyst poisons (A)</p> Signup and view all the answers

What occurs during the surface adsorption theory in heterogenous catalysis?

<p>Reactant molecules adsorb onto the surface and are transformed (D)</p> Signup and view all the answers

Which statement is true about the effect of increasing the amount of catalyst?

<p>It has little effect on the rate of the reaction (B)</p> Signup and view all the answers

What is the definition of Activation Energy?

<p>The energy required for effective collisions between particles to occur. (A)</p> Signup and view all the answers

What does a Reaction Profile Diagram illustrate?

<p>The energy change of a chemical reaction as it progresses with time. (A)</p> Signup and view all the answers

How does a catalyst affect the Activation Energy of a reaction?

<p>It reduces the Activation Energy needed for the reaction. (A)</p> Signup and view all the answers

What typically happens to the rate of reaction as the temperature increases?

<p>The rate of reaction increases exponentially. (C)</p> Signup and view all the answers

What observable change occurs in the conical flask during the reaction between sodium thiosulfate and hydrochloric acid?

<p>A precipitate is formed, indicating the presence of sulfur. (D)</p> Signup and view all the answers

If the concentration of sodium thiosulfate is halved, what effect does this have on reaction times?

<p>Reaction times double compared to original values. (C)</p> Signup and view all the answers

Which of the following best explains the term 'rate of reaction'?

<p>It is defined as the change in concentration per unit time of one reactant or product. (C)</p> Signup and view all the answers

What effect does increasing temperature generally have on particle collisions?

<p>It increases the energy of the collisions. (C)</p> Signup and view all the answers

Flashcards

Reaction rate

The speed at which a chemical reaction occurs.

Instantaneous rate

The rate of a reaction at a specific point in time.

Factors affecting reaction rate

Several aspects influence how quickly a reaction happens.

Nature of reactants

The type of chemical bonds involved in the reaction affects the speed.

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Particle size

Smaller particles lead to faster reaction rates due to increased surface area.

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Concentration

Higher concentration of reactants leads to faster reactions.

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Temperature

Higher temperature leads to faster reactions.

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Catalyst

Substances that speed up reactions without being consumed.

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Catalytic converter

A device in a car's exhaust system that uses catalysts to convert harmful pollutants into less harmful substances.

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Catalyst poisoning

When a substance deactivates a catalyst, preventing it from working properly.

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Effective collision

A collision between reacting particles that results in the formation of products.

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Activation energy

The minimum amount of energy required for a collision between reacting particles to be effective.

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Adsorption

The process where molecules attach to the surface of a catalyst.

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Desorption

The process where products detach from the surface of a catalyst.

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How does a catalytic converter work?

Catalytic converters use catalysts like platinum, palladium, and rhodium to convert harmful pollutants (e.g., carbon monoxide, nitrogen oxides, hydrocarbons) in car exhaust into less harmful substances like carbon dioxide, nitrogen, and water.

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Homogenous Catalysis

A type of catalysis where the catalyst and reactants exist in the same physical state (e.g., liquid, gas).

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Heterogenous Catalysis

A type of catalysis where the catalyst and reactants exist in different physical states (e.g., solid catalyst, gaseous reactants).

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Autocatalysis

A special type of catalysis where one of the products of a reaction acts as a catalyst for that same reaction.

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Intermediate Formation Theory

In this theory, a catalyst works by forming a temporary intermediate compound. This intermediate then reacts to produce the final products and regenerate the catalyst.

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Surface Adsorption Theory

This theory explains heterogenous catalysis, where reactants stick to the surface of a solid catalyst aiding the reaction.

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What happens to a catalyst's amount during a reaction?

A catalyst is not consumed during a reaction; it remains chemically unchanged. Therefore, its amount stays the same.

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What is the effect of a catalyst on equilibrium?

A catalyst does not affect the position of equilibrium. It only speeds up the rate at which equilibrium is reached.

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Reaction Profile Diagram

A graph showing how the energy of a reaction changes over time.

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What does a catalyst do on a reaction profile diagram?

A catalyst lowers the activation energy of a reaction, making it easier to occur.

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How does temperature affect reaction rate?

Higher temperature increases reaction rate because it gives reactant molecules more energy to overcome activation energy and collide effectively.

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What does a reaction profile diagram show about a catalyst?

It shows that the activation energy is lower than the original reaction, but the energy difference between reactants and products remains the same.

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Relate rate to concentration

Rate of reaction is directly proportional to the concentration of reactants.

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How to measure reaction rate

Measure the change in concentration of a reactant or product over time.

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How do you find the reaction time?

It's the time it takes for the reaction to reach a specific observable stage (e.g., when a solution turns cloudy).

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Rate of reaction

The change in concentration of a reactant or product over time, indicating how quickly a reaction proceeds.

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Why NaCl and AgNO3 react instantly?

Both sodium chloride (NaCl) and silver nitrate (AgNO3) are ionic compounds, meaning they readily dissociate into ions in solution. When mixed, the silver ions (Ag+) react quickly with chloride ions (Cl-) to form a solid precipitate, silver chloride (AgCl), which is insoluble in water, leading to the immediate formation of a visible product. The reaction is driven by the formation of this insoluble product.

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Increasing reaction rate

By increasing pressure or temperature, you can speed up a reaction. Higher pressure forces molecules closer together, increasing collisions and their energy. Higher temperature increases molecules’ kinetic energy, making them more likely to collide and react.

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Measuring reaction time

To measure the reaction time of a reaction, you can observe a change in a visible property. For example, you can monitor the time it takes for a cross to become invisible as a reaction forms a precipitate that obscures it.

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Rate's dependence on concentration

The rate of a reaction is directly proportional to the concentration of the reactant. This means that a higher concentration of a reactant leads to a faster reaction rate. The rate increases in a linear way as concentration increases.

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Dust explosion conditions

For a dust explosion to occur, combustible particles must be present, dry, mixed with oxygen, and exposed to a source of ignition.

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Higher concentration, faster reaction

Increasing the concentration of reactants in a reaction makes the reaction happen faster because there are more particles to collide and react.

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Temperature effect on reaction rate

Higher temperatures increase the reaction rate because particles have more energy, causing more collisions and more effective collisions.

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Sodium thiosulfate reaction experiment

This experiment investigates how changing the concentration of sodium thiosulfate affects the rate of its reaction with hydrochloric acid.

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Graphing reaction rate

Plotting the inverse of time (1/time) against the concentration helps visually show the relationship between reaction rate and concentration.

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Conclusion from the graph

The experiment's graph likely shows that as the concentration of sodium thiosulfate increases, the reaction rate also increases.

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Understanding the relationship

The experiment demonstrates that a higher concentration of reactants leads to a faster reaction rate.

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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

  • Materials: 5 cm³ of hydrogen peroxide, diluted to 50 cm³ water, 0.5g manganese(IV) oxide, conical flask, small test tube, thread, stopper, graduated cylinder, delivery tube, beehive shelf, teat pipette, stop clock

  • Procedure:

    • Measure and dilute hydrogen peroxide. Put in conical flask.
    • Weigh and suspend manganese(IV) oxide in the flask. Avoid contact between the two.
    • Fill a graduated cylinder with water and invert it over a beehive shelf. Fill the cylinder with air until the water level reaches 10 cm³.
    • Position the delivery tube of oxygen to allow it to collect in the cylinder.
    • Start the stop clock when the manganese oxide contacts the hydrogen peroxide by shaking the flask vigorously.
    • Record the total volume of oxygen in the cylinder every 30 seconds.

  • Data Table: (Time (mins), Volume O₂ (cm³))

  • Analysis: Graph total volume of oxygen against time.

Instantaneous Rate of Reaction

  • The 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:

    • The type of bonds involved (ionic or covalent), influences the difficulty to break these bonds before a reaction occurs.
    • Ionic bonds are fast, whereas covalent bonds are slower.

  • Particle Size: Smaller particles have a higher surface area and collide more frequently, leading to faster reactions. Finely divided substances react more quickly than large pieces.

    • Dust explosions can occur from finely divided particles. Conditions for dust explosions include: combustible particles, a source of ignition, dry particles, and oxygen presence.

  • Concentration: Higher concentrations of reactants lead to faster reaction rates because more particles mean more frequent collisions.

  • Temperature: Increasing the temperature increases the number of collisions and collision energy, resulting in a faster reaction rate. There's an exponential relationship between temperature and rate.

Catalysts

  • Definition: A catalyst is a substance that alters the rate of a reaction but is not consumed in the reaction.
  • Catalysts work in specific ways, functioning in small quantities, but not changing the overall reaction rate when there's an increase in the amount of the catalyst.
  • General Properties: Catalysts: They participate in reactions, are recovered chemically unchanged afterward, are specific to reactions, and need a very small amount to function. Catalysts may be poisoned by substances e.g., lead. A catalyst speeds up the rate of equilibrium.
  • Types of Catalysts:
    • Homogenous catalysis: Both reactants and the catalyst are in the same phase (e.g., iodine snake experiment).
    • Heterogenous catalysis: Reactants and catalyst are in different phases (e.g., oxidation of Methanol to Methanal).

Autocatalysis

  • Autocatalysis is a type of catalysis in which one of the products of the reaction acts as a catalyst for the reaction.

Mechanism of Catalysis

  • Intermediate Formation Theory: A catalyst forms an intermediate compound which is crucial in the decomposition reaction, for example, the decomposition of hydrogen peroxide catalyzed by I⁻ ions.
  • Surface Adsorption Theory: Molecules accumulate on the surface, which leads to collisions that break and form new bonds initiating a reaction.

Catalytic Converters

  • A catalytic converter is a device in a vehicle's exhaust system that converts harmful pollutants in exhaust gases to less harmful substances using catalysts like platinum, palladium, and rhodium.

Collision Theory and Activation Energy

  • Effective collisions occur when particles collide with enough energy to overcome the activation energy (minimum energy required for reaction).
  • Activation energy is the minimum energy needed for a reaction to occur.
  • The size of the activation energy depends on the nature of the reactants.

Reaction Profile Diagrams

  • Reaction profile diagrams show the change in energy during a reaction.
  • Endothermic reactions absorb energy, the reactants have less energy than the products.
  • Exothermic reactions release energy, the reactants have more energy than the products.
  • Catalysts reduce the activation energy for a reaction.

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Rates of Reactions PDF

Description

This quiz covers the concept of rates of reactions in chemistry, focusing on an experiment to monitor oxygen production from hydrogen peroxide using manganese(IV) oxide. Students will learn essential laboratory techniques and understand the factors affecting reaction rates.

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