Rate and extend the of chemical change

• How is rate of reaction calculated?

  Rate of reaction = amount of reactant used / time
• What are the units for rate or reaction?

  g/s , cm3/s , mol/s
• Name three common ways of measuring the rate of reaction.


  Loss in mass of reactants

  volume of gas produced

  Time for a solution to become opaque
• how to find a rate of reaction at some time, T, from a graph of amount of reactant vs time?

  pick a point corresponding to the time and find the tangent to its curve.

  find the gradient of the tangent.
• What does the rate of reaction tell us?

  How quickly the reaction takes place.
• what do rate graphs show?

  How the amount of given substance changes throughout a reaction.
• What factors affect rate of reactions?

  Temperature, pressure/concentration, surface area and catalysts.
• Explain collision theory?

  Reactant particles must collide with sufficient energy and proper orientation for a chemical reaction to occur.
• in terms of collision theory, what increases rate of reaction?

  More successful collisions in a given amount of time or a lower activation energy.
• Define activation energy.

  Energy required to break the bonds of reactants so products can be formed.
• What happens if particles don’t have enough activation energy?

  They don’t react and instead bounce if each other. This is an unsuccessful collision.
• What happens if there is enough activation energy?

  Reaction occurs as theres enough energy to break bonds so new ones can form. This is a successful collision.
• How does increasing the temperature increase the rate of reaction?

  Reactant particles move more quickly, they have more energy, particles can collide more successfully increasing the rate of reaction because more particles have a energy greater/equal to the activation energy.
• How does increasing the concentration and pressure affect the rate of the reaction?


  There would be more particles per unit of volume making it more crowded, this increases the change of particles colliding creating more sucked up collisions per second increasing the rate of reaction.
• How does increasing the surface area affect the rate of reaction?

  Increasing the surface area means the substance is separated into smaller parts. More particles would be exposed to the other reactant giving them a greater chance of collision creating more frequent successful collisions increasing the rate of reaction.
• How do catalysts affect the rate of reaction?

  A catalyst lowers the activation energy so more particles have a sufficient amount of energy for a successful collision making collisions more frequent increasing the rate of reaction.
• Which experiments can determine the effects on rates of reaction?

  gas collection, opaque reaction mixtures.
• Steps of gas collection *REQUIRED PRACTICAL*

  1. Clean a strip of magnesium with emery paper

  2. Place the strip into a conical flask containing 25 cm3 of a 0.1g/cm3 solution of hydrochloride acid

  3. Immediately, seal the flask with a bung that has a delivery tube connected to a gas syringe inserted through the centre

  4. Start a timer, every 10 seconds record the volume until the reactions stop (readings become consistent)

  5. Record the time of the first reading at which the gas syringe stopped increasing

  6. Repeat these steps increasing the concentration of hydrochloride acid by 0.1g/cm3 each time until the acid reaches 1g/cm3
• Steps of opaque reaction mixtures (disappearing cross) *REQUIRED PRACTICAL*

  Place a white tile with a black x painted under a glass beaker. Pour 25cm3 of sodium thiosulfate into the beaker. Add 25cm3 of a 0.1g/cm3 solution if hydrochloric acid. Immediately start a timer. Watch the black X from above the beaker and stop the timer once the cross ‘disappears’. record the time on the timer and repeat these steps increasing the concentration of hydrochloric acid by 0.1g/cm3 until the acids reached 1g/cm3.
• What is it called when the reaction can go backwards (products to reactants)?

  Reversible reaction.
• How are reversible reactions balanced?

  Equalibrium.
• How does energy change correlate with reversible reactions?

  The reactions have opposing energy changes They have the same energy released or gained but one reaction is endothermic whilst the other is exothermic.
• What is one of the circumstances needed for equilibrium?

  A sealed container.
• What is Le Chateliers principle?

  Le Chatelier's principle states that when a system at equilibrium is subjected to a change, it will adjust to minimize the effect of that change. It's all about maintaining balance.
• What does it mean for concentrations to be constant but not equal in equilibrium?

  In an equilibrium, concentrations of reactants and products remain constant, but they may not be equal to each other.
• In equilibrium are concentrations equal?

  Not necessarily.
• In equilibrium are concentrations constant?

  Yes
• How does temperature affect a reaction according to Le Chatelier's Principle?

  According to Le Chatelier's Principle, an increase in temperature favors an endothermic reaction and a decrease in temperature favors an exothermic reaction.
• How does Le Chatelier's Principle explain the effect of temperature on equilibrium?

  Le Chatelier's Principle states that if you increase the temperature, the equilibrium will shift in the direction that absorbs heat, while decreasing the temperature will cause the equilibrium to shift towards the direction that releases heat.
• How does pressure affect a reaction according to Le Chatelier's Principle?

  According to Le Chateliers Principle, an increase in pressure favours the side of the reaction with fewer moles of gas, while a decrease in pressure favours the side with more moles of gas.
• Front: How does Le Chatelier's Principle explain the effect of pressure on equilibrium?

  Back: Le Chatelier's Principle states that if you increase the pressure, the equilibrium will shift towards the side with fewer moles of gas, while decreasing the pressure will cause the equilibrium to shift towards the side with more moles of gas.
• How does concentration affect a reaction according to Le Chatelier's Principle?

  According to Le Chatelier's Principle, an increase in concentration of a reactant will shift the equilibrium towards the side that consumes that reactant, while a decrease in concentration of a reactant will shift the equilibrium towards the side that produces more of that reactant.
• How does Le Chatelier's Principle explain the effect of concentration on equilibrium?

  Le Chatelier's Principle states that if you increase the concentration of a reactant, the equilibrium will shift towards the side that consumes that reactant, while decreasing the concentration of a reactant will cause the equilibrium to shift towards the side that produces more of that reactant.
• What three factors effect equilibrium?

  Temperature, pressure, concentration.
• Define equilibrium.

  Equilibrium is a state where the forward and reverse reactions occur at the same rate. It's like a balance point where the concentrations of reactants and products remain constant. At equilibrium, there is no net change in the amounts of substances involved.