C6 The rate and extent of chemical change Flashcards
What are the two experiments used to investigate how concentration affects the rate of reaction?
Magnesium and hydrochloric acid: Measures the rate of reaction by collecting hydrogen gas.
Sodium thiosulfate and hydrochloric acid (Disappearing Cross): Measures reaction rate by observing cloudiness.
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What factors affect the rate of a chemical reaction?
Concentration of reactants (more particles = more frequent collisions).
Pressure of gases (higher pressure = more collisions).
Surface area of solids (smaller pieces = more surface exposed).
Temperature (higher temperature = faster particle movement and more collisions).
Catalysts (lower activation energy, speeding up the reaction).
What are the independent, dependent, and control variables in both experiments that investigate the rate of reaction
Independent variable (what is changed):
Magnesium experiment: Concentration of hydrochloric acid.
Sodium thiosulfate experiment: Concentration of sodium thiosulfate.
Dependent variable (what is measured):
Magnesium experiment: Volume of hydrogen gas produced.
Sodium thiosulfate experiment: Time taken for the cross to disappear.
Control variables (what stays the same):
Temperature (same room).
Volume of acid (use a measuring cylinder).
Surface area of magnesium / depth of liquid (use same-sized strips, same flask).
What results are expected in both experiments investigating the rate of reaction?
Magnesium & Acid: A higher acid concentration produces more hydrogen gas faster.
Sodium Thiosulfate & Acid: A higher sodium thiosulfate concentration makes the cross disappear more quickly.
How does temperature affect the rate of reaction?
Higher temperature = faster particles, more frequent & energetic collisions.
More collisions exceed activation energy, increasing the rate.
What is the method for the magnesium and hydrochloric acid experiment?
Measure 50 cm³ of hydrochloric acid into a conical flask.
Add a strip of magnesium ribbon and place a gas syringe with a bung.
Start a stopwatch and record the volume of hydrogen gas collected every 10 seconds.
Repeat with different concentrations of acid, keeping other variables the same.
Plot a graph of gas volume vs. time to compare reaction rates.
What is the method for the sodium thiosulfate and hydrochloric acid experiment?
Measure 50 cm³ of sodium thiosulfate into a conical flask.
Place it on a piece of paper with a black cross.
Add 10 cm³ of hydrochloric acid and start the stopwatch.
Stir gently and record the time taken for the cross to disappear.
Repeat with different concentrations of sodium thiosulfate.
What is collision theory and activation energy?
Collision theory: Reactions happen when particles collide with enough energy.
Activation energy: The minimum energy needed for a reaction to occur.
What is a catalyst, and how does it affect reaction rate?
A catalyst speeds up a reaction without being used up.
It provides an alternative pathway with lower activation energy.
Different reactions need different catalysts.
Enzymes act as biological catalysts.
How do concentration, pressure, and surface area affect the rate of reaction?
Higher concentration: More particles = more collisions.
Higher pressure: Particles closer together = more collisions.
Larger surface area: More exposed particles = faster reaction.
What is dynamic equilibrium?
When the forward and reverse reactions occur at the same rate in a closed system.
. What is a reversible reaction?
A reaction where the products can react to form the original reactants.
Example: Ammonium chloride ⇌ ammonia + hydrogen chloride.
What happens when you change the concentration of a system at equilibrium?
Increase reactant concentration → more products formed.
Decrease product concentration → more reactants react.
How does temperature affect equilibrium?
Increase temperature: Favors endothermic direction.
Decrease temperature: Favors exothermic direction.
How does pressure affect equilibrium in gases?
Increase pressure: Equilibrium shifts to side with fewer molecules.
Decrease pressure: Equilibrium shifts to side with more molecules.
How can you determine the rate of reaction from a graph?
Steeper gradient = faster reaction.
Flat section = reaction stopped.
Tangent method: Draw a tangent and calculate gradient (HT only).
