Topic 7- rates of reactions Flashcards
Describe the core practical in which we observe a colour change
Put 50cm3 of sodium thiosulfate solution in a flask.
Measure 5cm3 of dilute hydrochloric acid in a small measuring cylinder.
Add the acid to the flask and immediately start timer. Swirl the flask to the mix the solutions and place it on a piece of paper marked with a cross. When the cross disappears stop the clock and note time
Repeat using different concentrations of sodium thiosulfate,
How can the rate of a reaction be measured
By the rate at which a reactant is used up, or the rate at which a product is formed.
Measure the rate at which a reactant is used up and measure the rate at which a product is formed.
What 2 things do we measure when measuring rates of reactions
The mass of a substance- solid, liquid or gas- is measured with a balance.
The volume of a gas is usually measured with a gas syringe, or sometimes an upside down measuring cylinder or burette
Rate of reaction equation
Amount of reactant used or product formed DIVIDED by time taken
How do reactions occur and how can they be increased
Particles colliding and the rate if reaction is increased when the the frequency and/or energy of collisions is increased
How can temperature effect rate of reaction
A higher temperature means particles have more kinetic energy and therefore means more frequent collisions
How can concentration increase rate of reaction
An increased concentration increases rate of reaction because the particles are closer together and there are more of them
How can surface area to volume ratio effect rate of reaction
An increased surface area increases rate of reaction
What is a catalsyt
A substance that speeds up the rate of a reaction without altering the products of a reaction, being itself unchanged chemically and in mass at the end of a reaction
What effect does a catalyst have on energy
Increases rate of reaction by lowering activation energy
What are enzymes
biological catalysts which are used in the production of alcoholic drinks
What are the advantages of catalysts
Speeds up rate
Reusable, initial expense is repaid
Lower activation energy means less money spent on energy
List examples of where heat energy accompanies changes
-Salts dissolving in water
-Neutralisation reactions
-Displacement reactions
-Precipitation reactions
When these reactions take place in solution, temperature changes can be measured to reflect the heat changes
What is an exothermic reaction
a reaction/change in which heat energy is given out
What is an endothermic reaction
a reaction/change in which heat energy is taken in
