Chapter 6 Flashcards
Physical change
If substance changes state or it gets added to mixture -> no new substance are made + changes can be reversed
Chemical change
New substabce are made (reactants -> products) + changes aren’t reversible
Collision theory: collision frequency and energy transferred during collisions
- What the rate of a chemical reaction depends on
1. Collision frequency: more collision=fastee reaction - Partciles per unit volume: particles collide more frequently
2. Energy transferred during collisions: particles have to collide with enough energy for collision to be succesful -> succesful collisions ends in particles reacting to form products
Activation energy
Minimum amount of energy particles need to react (need this much energy to break bonds in reactants and start reaction) -> greater activation energy=more energy neede to start reaction
Factors affecting rate of reaction: increasing temperature
. Increases rate of reaction
- Higher temperature increase kinetic energy of particles (move faster)
. Increases energy of collisions -> more succcesful collsions
. Increases frequency of collisions
Factors affecting rate of reaction: increasing concentration/pressure
Increasing the concentration of a solution OR the pressure of a gas= increases rate of reaction
. Concentrated solution: more particles of reactant in sams unit of volume -> increases frequency of collisiom
. Increasing pressure of gas: more particles in same volume -> increases frequency of collisions
Factors affecting rate of reaction: Increasing surface area
Increasing surface area= increases rate of reaction
. More particles exposed so more partciles to react with -> increases frequency of collisions
Factors affecting rate of reaction: catalyst
Adding a catalyst= increases rate of reaction -> without being chemically changed or used up by the reaction
. Work by decreasing the activation energy needed for a reaction to occur by providing an alternative reaction pathway with lower activation energy -> more particles have activation energy so there’s more succesful collisions
. Enzymes: biological catalysts (work in living cells) -> high temperatures and extreme pH values can denature enzyme (doesn’t catalyse)
How to calculate the rate of reaction
Amount of reactant used OR product formed divided by time
Measuring rate of reactions that produce gas: volume of gas given off
Use of gas syring to measure volume of gas given off -> more gas given off during set time interval = faster reaction
. Rate of reaction units: cm^3/s
Measuring rate of reactions that produce gas: change in mass
- Place fask where reaction taking place onto mass balance -> putting cotton wool in the top flask allows gas to escape but keeps acid from spitting out
- As gas is released , there’s a loss in mass -> faster mass drops = faster reaction
. Rate of reaction units: g/s
Reversible reactions
Reactions that can be reversed where both the forward and reverse reactions happen at the same time -> if reaction endothermic in one direction then it will be exothermicin the other direction
Changing conditions of reversible reactions
The direction of the reaction depends on the reaction conditions -> changing reaction conditions (eg by heating or adding water) can change the direction of the reaction
Equilibrium
A state of balance that can occur for any reversible reaction in a closed system
- Rate of forwards reaction = rate of backwards reaction
- Concentration of A and B are contsant
Decrease of concentration of recatants (equilibrium)
Shift backwards to reduce the products and increase reactants
