Topic 7 Flashcards
(41 cards)
What is the formula to work out reaction rate?
Amount of reactant used/amount of produce formed/ time
How would you measure reaction rate with the cross on paper method and what is one problem with this method?
- mix two reactant solutions and put the flask on a piece of paper with a cross on it
- Observe the mark through the mixture and measure how long it takes for the mark to be obscured
Different people may not agree on when the cross disappears - need someone constant to measure time
How would you measure reaction rate using the change in mass method and what is one problem with this method?
- use a mass balance to measure rate of a reaction that produces a gas
- As gas is released, lost mass is easily measured on balance
- reaction has finished when the reading on the balance stops changing. stopwatch can measure how long it takes to reach this point
The method may produce harmful gases, so it must be done in a fume cupboard
How would you measure reaction rate using the gas syringe method?
- use a gas syringe to measure the volume of gas given off in a reaction
- Reaction has finished when no more gas is produced. Use stopwatch to measure how long it takes to reach this point
(gas syringe method) If more gas is given off during a set time interval, does that mean the faster the reaction or the slower the reaction?
The faster the reaction
(change in mass method) If the mass reading drops more slowly, does that mean the faster the reaction or the slower the reaction?
The slower the reaction
Describe how you would carry out the marble chip reaction rate experiment (SURFACE AREA)?
- set up apparatus (gun)
- measure volume of gas produced and take readings at regular intervals
- Plot graph (volume against time)
- Repeat experiment with exactly the same volume/ conc of acid, and mass of the chips, but use different sized chips
- Repeat experiment and compare reaction rates between different sized chips
Why does using finer particles in this experiment, increase the rate of the reaction? (dont explain, just state in this question)
finer particles means a larger surface area.
What would you expect to happen in the marble chip experiment, if you measure how concentration affects the rate of the reaction? (state)
The reaction with the highest acid concentration would be fastest
Describe how you would measure the affect of temp on the rate of a reaction using the cross on paper method? Also, what must you control in the experiment?
- Measure fixed volumes of sodium thiosulfate and HCl, using a measuring cylinder
- Use a water bath to gently heat both solutions to a desired temp
- Mix solutions and place them over a black cross and watch the mark disappear through the cloudy, yellow sulfur over time
- plot results on a time against temperature graph
- You must control the depth and volumes of liquid and the concentrations of the solutions
Does heating a solution to a higher temp, increase the rate of a reaction or decrease the rate of a reaction?
It increases the rate of a reaction
What is the formula to work out gradients?
Gradient = change in y/change in x
How would you work out the gradient of a curve?
You would draw a tangent at the point that you want to find the gradient. You would then use( gradient = change in y/change in x) with any of the 2 points on the tangent
What 2 things does the rate of a chemical reaction depend on?
- collision frequency - how often there are successful collisions
- energy transferred during a collision - particles need to collide with atleast the activation energy (minimum energy needed in a reaction) to be successful
What does more collisions mean in terms of reaction rate?
More collisions means the higher the rate of a reaction
What three things increases reaction rate? (outline)
- higher temperature
- Higher conc/pressure
- Smaller solid particles (more surface area)
How does increasing temperature increase rate?
- When temp increases, the particles move faster. This means they’re going to have more collisions
- They also increase the energy of the collisions and reactions can only happen if the particles collide with enough energy
How does increasing conc/pressure increase rate?
- if a solution is more concentrated, it means there are more particles of the reactant in the same volume. This makes collisions more likely
- In a gas, increasing the pressure means that particles are more crowded. This means that collisions between particles would be more likely
How does increasing surface area/ breaking a solid into smaller bits increase rate?
The particles around a broken up solid would have more area to work on, so the frequency of collisions would increase
What is a catalyst?
A catalyst is a substance that increases the rate of a reaction without being chemically changed or used up in the reaction
How do catalysts increase the rate of a reaction?
They reduce the activation energy needed for a reaction to take place by providing an alternative reaction pathway and as a result, more particles have at least the minimum amount of energy needed for a reaction to occur when the particles collide
What are enzymes?
They are biological catalysts - they speed up the chemical reactions in living cells
What reactions are catalysed by enzymes? (3)
- respiration
- photosynthesis
- Protein synthesis
Give an example of how enzymes are used in the fermentation of yeast cells to make alcoholic drinks?
They catalyse the reaction that converts sugars into ethanol and carbon dioxide
