C7 Rates of reaction Flashcards
What are enzymes?
biological catalysts
What are enzymes used in the production of?
alcoholic drinks
What is a reaction profile graph?
a graph that shows how the energy in a reaction changes as the reaction progresses
y axis - energy
x axis - progression of reaction
What does a reaction profile start and end with?
- starts with energy level of reactants
- ends with energy level of products
What are the two ways you can calculate overall energy change?
overall evenergy change
= reactant energy - products energy
= bond breaking energies - bond forming energies
What will be the energy levels of reactants and products in an exothermic reaction?
- reactants have more energy than products
- energy is being released to the surroundings
What will be the energy levels of reactants and products in an endothermic reaction?
- reactants have less energy than products
- energy is being absorbed from the surroundings
What is activation energy?
minimum amount if energy particles need when they collide in order to react
What are the factors that affect the rate of reaction?
- temperature
- concentration of dissolved reactants
- pressure of gas reactants
- surface area of solid reactants
- using a catalyst
How does temperature affect particle collision? (therefore affecting RoR)
- as temp increases, RoR increases
- at higher temp particles have more kinetic energy
- move faster and more likely to collide with other particles
- when particles collide they do so with energy
- so the frequency of successful collisions increases
How does concentration affect particle collision? (therefore affecting RoR)
- as conc of a dissolved reactant increases, RoR increases
- higher conc, more particles in the same amount of space
- frequency of collisions increases
- so particles are more likely to react
How does surface area affect particle collision? (therefore affecting RoR)
- as the surface area of a solid increases, RoR increases
- increased area for particles to collide with
- frequency of collisions increases
- greater chance of reaction
How will using a catalyst affect rate of reaction?
- using a catalyst lowers the activation energy
- more particles have the minimum energy needed for a reaction to occur when they collide
- increases RoR
What are the properties of catalysts?
- do not proudce more product
- do not get used up in reaction
- do not get chemically changed
- small amounts will catalyse large amounts of reactants
- save time in industry, reducing energy use and thus reduces fuel use and pollution
- enzymes are biological catalysts
- reusable
What are the two ways of calculating the mean rate of reaction?
mean RoR = quantity of reactant used/time
mean RoR = quantity of product used/time
What do steep/flatter/horizontal lines on a reaction profile tell us?
- steep: reaction fastest
- flatter: slower RoR
- horizontal: reaction stopped
How do you calculate RoR from a graph?
RoR = gradient=change in y/change in x
- draw a tangent to given point
- pick two points on the tangent
- calculate the gradient
When a chemical reaction occurs, energy will be __________ to or from the ________ energy store if the products depending on the ________ energy store of the reactants.
- transferred
- chemical
- chemical
If the products in a chemical reaction transfer thermal emergy to the surroundings, the temperature of the surroundings will ________.
increase
If the products in a chemical reaction transfer thermal emergy from the surroundings, the temperature of the surroundings will ________.
decrease
Exothermic reactions ________ thermal energy ____ the surroundings. The temperature of the surrounding will ________.
- release
- into
- increase
Endothermic reactions ________ thermal energy ____ the surroundings. The temperature of the surrounding will ________.
- absorb
- from
- decrease
How can we experiment to test if a reaction is endo- or exo- thermic?
- use a measuring cylinder to measure 50cm^3 of water
- pour the water into the polystyrene cup
- put the polystyrene cup into a beaker that has been padded with cotton wool
- measure the initial temperature of the water
- add the solid and stir gently for 5 mins
- measure the final temperature of solution
- work out is the temperature increased or decreased
How can we improve method of measuring whether a reaction is endo- or exo- thermic?
-add a lid
–to reduce heat transfer to the surroundings
-add cotton wool to beaker
–to reduce heat transfer to surroundings
What does the amount of energy released or absorbed in a reaction depend on?
how much reactant is used
What do we need to do to get bonds between molecules to break?
supply energy
What happens when new bonds are formed?
energy is released
Bond breaking is a _________ process and why?
- endothermic
- energy us being absorbed from surroundings
- to break existing bonds
Bond forming is a _________ process and why?
- exothermic
- energy is being released to the surroundings
- when new bonds are made
What happens in exothermic reactions?
- bonds formed
- energy released > energy used to break old bonds
- leftover energy released to surroundings
- temperature of the surroundings increases
What happens in endothermic reactions?
- bond breaking
- energy needed to break bonds > energy released when new bonds are formed
- the extra energy needed is absorbed from the surrounding
- temperature of surroundings decreases
What do positive and negative energy changes indicate?
negative - exothermic
positive - endothermic
