Rates of Reaction and Energy Changes Flashcards
What factors affect reaction rate?
- Temperature
- Surface area
- concentration
- pressure
Give an example of a practical to show reaction rate with change of temperature
- Take fixed volumes of sodium thiosulfate solution and hydrochloric acid
- Put the sodium thiosulfate in a conical flask
- Put the hydrochloric acid in a test tube
- Put both of these in a water bath until it heats to a desired temperature.
- Mix the solution in the conical flask and start a timer.
- Place the conical flask over a piece of paper with an X mark on it and measure how long it takes for the X mark to disappear through the yellow precipitate.
- Repeat with different temperatures, but keep the volume and concentration of liquid the same
Give the practical about how change in surface area affects rate
- Take a conical flask, put a bung on it to prevent loss of gases, attach a capillary tube through the hole and attach it to a gas syringe.
- Inside the conical flask, place marble chips in a set volume of hydrochloric acid and measure how much carbon dioxide is produced after set time intervals
- Repeat this test with the same temperature and concentration and volume, but with the marble chips more fine.
Give a practical about change of concentration in reaction rates.
- Take a mass balance, put a set volume of hydrochloric acid into the flask and add a set mass and surface area of marble chips.
- Put this flask onto the mass balance and see how much the mass changes over regular intervals
- Plot the mass change
- Repeat with different concentrations of hydrochloric acid.
What is the collision theory?
Rate of reaction depends on:
- Collision frequency
- The collision energy. The minimum energy that particles require to react on collision is the activation energy. Particles must collide with enough activation energy to react.
How does temperature affect rate of reaction?
- Temperature increase means that particles move faster, means more frequent collisions
- Temperature increase means that particles have more energy, more collisions are more likely to have the required activation energy to react.
How does concentration and pressure affect rate of reaction
- Solution is concentrated –> more particles of reactant in same volume –> makes collisions more likely –> rate of reaction increases
- High pressure –> particles are more crowded –> frequency of collisions increase –> rate of reaction increases
How does surface area affect rate of reaction?
- High surface area –> more area for the particles to react with –> rate of reaction is faster
What is a catalyst?
- Substance that increases rate of reaction without being chemically changed or used up in the reaction
How do catalysts work?
Catalysts decrease the activation energy for a reaction to occur(by providing an alternative reaction pathway with lower activation energy) –> more particles will have the minimum amount of energy –> higher rate of reaction
Where are enzymes used
Used to produce alcoholic drinks
- Enzymes from yeast cells are used in fermentation to make glucose into ethanol and carbon dioxide.
What is an exothermic reaction?
- Reaction which gives out heat energy to the surroundings, shown by a rise in temperature of the surroundings
- Bonds are made, so energy is given off
What is an endothermic reaction?
- A reaction which takes heat energy in from the surroundings, shown by a fall in temperature of the surroundings.
- Bonds are broken and the reaction requires energy to break bonds
Are these reactions endothermic or exothermic?
- Salts dissolving in water
- Neutralisation
- Displacement
- Precipitation
Dissolving salts in water: exothermic
Neutralisation: exothermic and endothermic
Displacement: exothermic
Precipitation: exothermic
What is the activation energy on a reaction profile?
- Difference between reactants and highest point on the curve
