Rates Of Reaction Flashcards
What does the graph for quantity of product formed (RoR Ch)
- what is on the y-axis
- what is on the x-axis
- shape of the curve
- Quantity of product formed in grams if solid/liquid and centimetres cubed if gas
- Time in Seconds
- rises quickly and curves off into a straight line horizontally.
Why does the graph for quantity of products formed look like that? (RoR Ch)
- initially, reaction if very fast. Lots of product in short amount of time because of a large number of reactant molecules so lots are reacting and forming.
- gradually, the slope of the line becomes less steep. The reaction is slowing down. **Rate **of Reaction is decreasing because lots of the reactant molecules have already reacted and turned into product. Fewer reactant molecules available to react.
- Finally, the slope is now at zero. The line is flat so at this point the reaction has stopped. All molecules have already reacted.
What does the graph for quantity of reactants present look like that (RoR Ch)
- what is on the y-axis
- what is on the x-axis
- shape of the curve
- Quantity of reactants in grams if solid/liquid and centimetres cubed if gas
- Time in Seconds
- Starts off decreasing quickly and starts to slow down until the reaction becomes a straight line.
Why does the graph for quantity of reactants used up look like that? (RoR Ch)
- Initially the rate at which the curve is dropping is fast. Lots of reactants are being used up in a short amount of time because a large number of reacting molecules are forming into products Leaving less reactants.
- gradually the slope becomes less steep but is still going down .The rate of the reaction is decreasing because lots of molecules have already reacted so fewer reactants left.
- the slope is now at zero so all molecules have reacted leaving no reactants left behind.
What is the unit for measuring the quantity of reactants/products used for solids and liquids? (RoR Ch)
Measure this in grams
What is the unit for measuring the quantity of reactants/products used for gases? (RoR Ch)
Centimetres cubed
What are the two ways of measuring rate of reaction?
- Using quantity of products formed
- Using quantity of reactants used
What is the equation to find the mean rate of reaction for quantity of products formed? (QC Ch)
Quantity of product formed (cm cubed or g) divided by the time in seconds
What is the equation to find the mean rate of reaction for quantity of reactants used up.
Quantity of reactant used up (cm cubed or g) divided by the time in seconds
What is the problem with a curved rate of reaction graph? (RoR Ch)
- the slope of the curve is constantly changing.
- which means that the rate is constantly changing.
- so it is difficult to get a clear idea of the rate of reaction at any specific point.
How do you fix the problem of finding the rate of a reaction from a curved and constantly changing graph? (Ror Ch)
Drawing a straight line which just touches the point we are interested in. Tangent. The slope of this line gives an idea of the rate of reaction.
How does the tangent drawn on a sloped graph help calculate the mean rate of reaction? And what are the units normally? (Ror Ch)
- From both sides of the line draw a triangle.
- Find out the length of both of the sides of this triangle.
- divide the y by the x.
- the units are normally grams / second.
What is the collision theory? (RoR Ch)
- Chemical reactions can only take place when the reacting particles collide with each other. The collisions must have sufficient energy.
- The rate of a chemical reaction is determind by the frequency of successful collisions.
- The word frequency means the number of successful collisions per second.
Explain, using collision theory, why the shape of a time, quantity of product graph is curved upwards and then trails off. (RoR Ch)
- Reactions are rapid initially becuase we have a large number of reactant molecules. this means that we have a large number of collisions per second.
- Over time reactions slow down because the number of reactant molecules is running out. That means that we have a smaller number of collisions per second
- Finally the reaction stops because all of the reactant molecules have run out. This means that the number of collisions per second is now zero.
what is the relationship between the rate of reaction and the concentration of reacting particles? (RoR Ch)
the rate of reaction is proportinal to the concentration.
What are the comparisons between the graph of a higher concentration of reactant and the lower concentration of reactant. (RoR Ch)
- The higher concentration is a faster reaction. We can tell this because the line is steeper.
- With the higher concentration you get more product at the end because we started with more reactant molecules at the start
What is a hypothesis? (RoR Ch)
a proposal that could explain a fact or an observation, in science a hypothesis must be testable.
What is the word equation for the dissapearing cross reaction?
sodium thiosulfate solution + hyrdochloric acid —> sulfur (solid)
What does the product sulfur in the dissappearing cross reaction do and what is the specific name for it? (RoR Ch)
The sulfur makes the solution go cloudy. This is called turbidity. We can use this to see how long the reaction takes to finish.
What is the method for the dissappearing cross reaction? (RoR Ch)
- Use a measuring cylinder to put 10cm cubed of sodium thiosulfate solution into a conical flask.
- place this onto a printed black cross
- 10cm cubed of hydrochloric acid into the conical flask.
- swirl the solution and start the stopwatch.
- look down through the top of the flask and after a certain time the solution will go cloudy.
- stop the clock when we can no longer see the cross.
- carry out the experiment again, using lower concentrations of sodium thiosulfate solution.
- repeat the whole experiment and calculate mean values for each concentration of sodium thiosulfate solution.
What does a reproducible experiment entail? (RoR Ch)
it is reproducable if it can be repeated by another person or using a different technique or equiptment and still get the same result.
Why might the dissappearing cross experiment not be considered as reproducible? (RoR Ch)
different people have different eyesights. meaning that some people can see the cross for longer than others so may not get the same result. however since all students use the same size printed cross, this problem may not be too great.
What are the two methods for measuring rate of reaction? (RoR Ch)
- The dissapearing cross method
- measuring the volume of a gas produced by a reaction.
What is the method for measuring the volume of gas produced by a reaction? (RoR Ch)
- Using a measuring cylinder to place 50cm cubed of hydrochloric acid into a conical flask.
- Attach the conical flask to a bung and delivery tube.
- place the delivery tube into a container filled with water.
- Place an upturned measuring cylinder also filled with water over the delivery tube.
- add a 3cm strip of magnesium to the hydrochloric acid and start the stopwatch.
- This produces hydrogen gas which os trapped inside the measuring cylinder.
- every ten seconds we measure the volume of hydrogen gas in the measuring cylinder. and continue until no more gas is given off.
- repeat the reaction, using different concentrations of hydrochloric acid.
