Topic 7 Flashcards
describe a practical investigating effects changing conditions of reaction on rates of chemical reactions by measuring production of a gas
- set up apparatus; marble chips with dilute HCl
- measure volume of gas produced using gas syringe, take readings at regular time intervals
- using finer particles means marble has larger surface area , so faster the reaction
- more finer particles means extra surface area gives faster rate and also more gas evolved overall
- higher concentration of acid gives faster reaction
describe a practical investigating effects changing conditions of reaction on rates of chemical reactions by observing a colour change
sodium thiosulfate and hydrochloric acid react to form a yellow precipitate of sulfur
- amount of time that it takes for coloured precipitate to form measures rate of reaction
- use water bath to gently heat both solutions to desired temp before mix them
- mix solutions in conical flask over black mark on paper
- time how long takes for mark to disappear
- increase temp increases reaction rate
determining he rate of a given reaction: precipitation
- mix 2 reactant solutions and put flask on paper that has mark on it
- observe mark through mixture and measure time taken for mark to be obscured
- faster disappears, faster reaction
- result is subjective,different people may disagree when mark disappears
determining he rate of a given reaction: change in mass
- as gas released, lost mass easily measured on balance
- quicker mass drops, faster reaction
- reaction finished when mass stops changing
determining he rate of a given reaction: volume of gas given off
- use of gas syringe to measure volume of gas given off
- more gas given off during set time interval, faster reaction
- reaction finished when no more gas produced
what does the the rate of a chemical reaction depend on
- collision frequency of reacting particles, more successful collisions,faster reaction
- energy transferred during collision, minimum energy particles need to react when collide called activation energy, particles need to collide with at least activation energy for collision be successful
what effect does increasing the temperature have on the reaction rate
- temp increased, particles move faster, so more collisions
- higher temp increases energy of collisions, as particles moving faster. so more successful collisions
- increasing temp,increases rate of reaction
what effect does increasing concentration and pressure have on the reaction rate
- more concentrated means more particles of reactant in same volume, collisions ore likely, so reaction rate increases
- in gas increasing pressure means particles more crowded, more frequent collisions, faster reaction rate
what effect does surface area to volume ratio have on the reaction rate
- if 1 reactant broken into smaller pieces surface area to volume ratio increase
- particles around it have more area to work on, frequency of collisions increases
- rate of reaction faster for solids with larger surface area to volume ratio
describe a catalyst
a substance that speeds up rate of reaction without altering the products of reaction, being itself unchanged chemically and in mass at end of reaction
what are enzymes
biological catalysts and used in fermentation process used to make alcoholic drinks
how do catalysts increase the rate of reaction
-by decreasing activation energy needed for reaction to occur, done by providing an alternate reaction pathway that has lower activation energy, so more particles have at least minimum amount of energy needed for reaction to occur when particles collide
what do changes in heat energy accompany
-salts dissolving in water
-neutralisation reaction
-displacement reaction
-precipitation reaction
when these reactions take place in solution, temperature changes can be measured to reflect heat changes
describe an exothermic reaction
reaction that gives out energy to surroundings, usually heat energy
describe an endothermic reaction
reaction which takes in energy from surroundings, usually heat energy
