Topic 7 - Rates Of Reaction And Energy Changes Flashcards
What is the equation for rate of reaction?
Rate of reaction = amount of reactant used/product formed / time
What units could be used for rate of reaction?
g/s
cm³/s
mol/s
How can you measure the rate of reaction when a gas is given off?
Measure time and collect gas in an upside down measuring cylider in trough of water/gas syringe to emasure vol of gas produced
Measure time and change in mass
How can you measure the rate of reaction when a precipitate is formed?
Put a black cross below a beaker containing one reactant. Time how long it takes for the cross to disappear after the secons reactant is added.
Why is using a precipitation method to investigate rate of reaction not very accurate?
Its subjective so people likely to disagree over exact pt cross no longer visible
How can you measure rate of reaction using a digital balance?
When a gas is produced as this will cause mass to decrease. The experiment can be carried out on a digital balance and rate of reaction can be calculated by recording the kass at regular time intervals.
What does ‘activation energy’ mean?
Minimum amount of energy required for a reaction to occur between 2 reacting particles
What must happen for a reaction to occur?
Particles must collide at the correct orientation with sufficient energy to react
In terms of particles, what 2 things could happen when the rate of reaction increases?
More frequent collisions
Energy of collisions increases
How can the rate of a reaction be increased?
Increase temp Increase concentration Increase SA to vol ratio Add catalyst Increase pressure (for gases)
How does temp affect the rate of reaction?
Increased temp increases rate of reaction.
Reactants have more energy so more particles have energy above activation energy.
More sucessful collisions.
More frequent collisions - particles = more KE
How does SA affect rate of reaction?
Increasing SA increases rate of reaction
Bigger SA = more exposed particles v more frequent successful collisions
How does a catalyst affect the rate of reaction?
Increases the rate of reaction.
Provides an alternate reaction pathway w lower activation energy.
More particles will have sufficient energy to overcome the activation energy + react = more sucessful collisions in same time
How does concentration affect rate of reaction?
Increasing concentration increases rate of reaction.
More reacting oarticles in same vol = more frequent successful collisions.
How does pressure affect rate of a gaseous reaction?
Increasing pressure increases rate of reaction.
More reacting particles in same vol of gas /same no of particles in smaller vol = more frequent sucessful collisions
Marble chips react with hydrochloric acid to produce calcium chloride, water and carbon dioxide. How could you measure the rate of reaction?
Use a digital balance to measure change in mass over a period of time (as carbon dioxide is released)
Marble chips react woth hydrochloric acid to produce calcium chloride, water and carbon dioxide. How could the rate of this reaction be increased?
Increase SA of marble chips by turning them into a powder.
Increase concentration of acid
Increase temp
After completing an experiment, how can you find the rate of reaction using a graph?
Plot:
X axis: time
Y axis: amount of reactant used/product formed
Draw tangent to pt on graph and find gradient of line
A graph showing time and amount of gas given off during an experiment has a steep gradient. What does this tell you about the rate of reaction?
Fast rate of reaction
A graph is plotted to show time and the amount of gas given off during a reaction. Describe the shape of the curve.
Initially curve is very steep as rate of reaction = fast at start.
Curve becomes less steep as reactants get used up because fewer successful collisions occuring.
At end, graph is flat line - all reactants have been turned into products.
What is a catalyst?
Substance which speeds up the rate of a reaction without being chemically changed at end
How does a catalyst speed up the rate of a reaction?
Provides an alternate reaction pathway w lower activation energy
What are enzymes?
Act as biological catalysts that increase the rate of reactions in living cells.
Which enzyme is used to produce ethanol from glucose?
Yeast
