Topic 7- Rates Flashcards
Exothermic Reaction
- Gives out energy
- Gives out heat
- Shown by a rise in temperature
- Mexo
Endothermic Reaction
- Takes in energy
- Takes in heat
- Fall in surrounding temperature
- Bendo
Activation Energy
The amount of energy required to start a reaction
Reaction Profiles
Show the starting energy of the reactants and the end energy of the products
Exothermic : Reactants higher than products
Endothermic : Products higher than reactants
Catalyst
- Increase the rate of a reaction
- Is not chemically changed in a reaction
- Will not change the products
- Provides an alternative reaction pathway
- Increase the rate of a reaction
Enzymes
- Biological Catlysts
- Speeee up chemical reactions in living cells
- Used in protein synthesis, respiration and photosynthesis
Rate of Reaction
How fast a reaction occurs. Can be worked by when all the reactants are used up or how quickly the products formed.
How to work out rate of reaction
Amount of reactant used or product formed over time
Precipitation experiment to measure rates
- Mixing two see through reactions forms a precipitate which clouds the solution
- Mix the two solutions on a piece of paper with an X on it
- Observe the mark until it can no longer be seen as it clouds
- The faster it disappears, the faster the rate
- This is subjective
Changes in mass to measure rates
- Gas needs to be measured using a mass balance
- As gas is released, lost mass is easily measured using the mass balance
- The quicker the drop, the faster the reaction
- ## The reaction bas finished when the balance stops changing
Gas Syringe
- Shows the volume of gas given off
- The more gas given off, the faster the reaction
- When no more gas is given off, the reaction has finished
Surface area rate
- Use an experiment using HCl and marble chips
- Measure the volume of gas produced using a gas syringe
- Take regular time readings
- Repeat the experiment with same mass of chips but different surface areas
- The larger the surface area, the quicker the reaction
Rates on a graph
- When the mass/volume produced reaches a constant, the reacton will have finished
- The steeper the gradient, the faster the reaction
Affect of concentration on rates
- The higher the concentration, the faster the rate
- Same effect as surface area
How temperature effects rates
- The rate can be measured by the reaction of hcl and Sodium Thiosulfate
- Both clear and when reacted from a yellow precipitate and sulfur
- Measure the amount of time it takes for the precipiate to form
- Use the X from the precipitation
- Use a water bath to heat the solution and maintain a constant
- Change the temperature to measure the time difference
Effect of temperature on rates
The highter the temperature, the higher the rate
The molecules have more energy and move around faster increasing the chances of successful collisons
Calculating rates
- Faster rates of reactions are shown by steeper gradients
- Gradient = Change in Y divided by change in x
Gradient of a curve
- At different points on a curve, the gradient will be different
- Draw a tangent at a certain point
- A tangent has the same gradient as the point
- Use the tangent as the gradient
Collision Theory
- Particles must collide with a certain amount of energy to react
- The more successful collisons, the faster the reaction
- These particles must have more than the activation energy to start the required reaction
Factors affecting rates
- Catalyst - Lowers activation energy
- Surfacee Area - More area to react
- Concentration- More reactants in a given volume
- Temperature - gives the molecules more energy to move around faster and create more successful reactions
Measuring temperature changes
- The change can be measured
- Put a polystyrene cup in a beaker with cotton wool for insulation to limit energy lost
- Add the first reagent and measure the intial temperature
- Add the second reagent
- Put a lid on the beaker to limit energy lost in evaporation
- Record the maximum and minimum temperature and then calculate the change
Bond Energies
- Energy must always be supplied to break bonds
- Endothermic produces a strong bond being broken whilst exothermic is opposite
- Exothermic releases energy and endothermic consumes energy
How to work out energy change
Energy required to break bonds - Energy released by bonds
Positive value means endothermic
Negative value means exothermic
Values will always be given in papers if needed
