Rates Of Reaction And Energy Changes Flashcards
What is the rate of reaction?
How quickly a reaction happens. Measures how quickly reactants are used up or how quickly products are formed
Give the equation for rate of reaction using products/product used/formed
Rate of reaction = amount of product used OR amount of product formed / time
Describe a precipitation experiment to follow reaction rates
1) works for any reaction where mixing 2 see through solutions form a precipitate, which clouds the solution
2) mix the two reactant solutions, put flask on piece of paper with mark on it
3) observe mark through mixture, time how long it takes for mark to be obscured. Faster disappears > faster reaction
4) result subjective: different people disagree on when mark disappears
Describe an experiment in change in mass (usually gas given off) to follow reaction rates
1) measures the rate of reaction that produces gas
2) having cotton wool in top of conical flask stops non gases escaping. As gas is released, lost mass measured on mass balance. Quicker reading on balance drops > faster reaction
3) reaction finished when balance reading stops changing
4) use results to plot graph of change in mass against time
5) if gas is harmful take safety precautions
Describe a experiment measuring volume of gas give off to follow reaction rates
1) use gas syringe to measure volume of gas given off
2) more gas given off during set time interval > faster reaction
3) tell reaction finished when no more gas produced
4) use results to poor graph of gas volume against time elapsed
5) use right size gas syringe to avoid damaging it
Practical: Describe ‘rate experiments using gases’ (measuring effect of surface area on rate using marble chips and hydrochloric acid)
1) marble chips in hydrochloric acid, in conical flask. Air tight (stops gas escaping) gas syringe system attached. Stop clock.
2) measure volume of gas produced using gas syringe, take readings st regular time intervals, record results
3) plot graph of results: x axis = time, y axis = volume
4) repeat experiment with same volume + concentration of acid, same mass of marble chips, but chips more crunched up
5) repeat with same mass of marble chalk. Sooner reaction finishes, faster rate of reaction. Steeper gradient of graph, faster rate of reaction. Flat graph, reaction is finished.
Using finer particles means marble has larger surface area, meaning faster reaction. Changing reactant concentration also affects reaction rate. Measure effect of concentration on rate by following same method but keep marble chips with same mass + surface area. Use different concentrations of acid. Higher concentration > faster reaction.
Can also measure rate of reaction by measuring loss of mass as gas is produced
Practical: Describe ‘rate experiments involving precipitation’
Reaction rate is affected by temperature
1) measure fixed volumes of sodium thiosulfate and hydrochloric acid, using measuring cylinder
2) using water bath, gently heat both solutions to desired temperature
3) mix solutions in a conical flask. Place flask over paper with mark on, time how long it takes mark to disappear
4) reaction can be repeated for different solutions at different temperatures.
Use results to measure what effect changing temperature has on rate of reaction (shorter length time taken > faster rate)
5) plot time taken for mark to diss appear against temperature of reacting solution
Increased temp > faster reaction
On graph of amount of product formed (or reactant used) against time: what does the gradient represenT?
The rate of reaction. Steeper slope > faster rate of reaction
How do you find gradient at certain point on curved gradient?
Draw tangent at that point. (Tangent = line that touches curve and has same gradient as line at that point)
When drawing tangent, space between line and tangent must be same on both sides of point
Rate at that point = gradient of tangent
What 4 main factors does rate of reaction depend on?
Temperature
Concentration
Pressure (for gases)
Size of particles (for solids)
What is a successful collision?
Collision ends in particles reacting to form products
What’s activation energy?
Minimum energy particle needs for bonds to break and particle to react upon collision
Increases number of collisions > increased rate of reaction
How does temperature affect rate or reaction?
Increased temperature > particles move faster > more collisions
Higher temperatures > increased energy of collisions > more successful collisions > increased rate
How does increased pressure or concentration affect rate?
Solution more concentrated > more particles of reactant in same volume > collisions more likely > rate increased
Gas, increase pressure > particles more crowded > frequency of collisions between particles increased > rate increased
How does surface area affect rate of reaction?
Solid reactant broken to smaller pieces > increased surface area to volume ratio > greater area exposed to particles around reactant > frequency of collisions increased > increased rate
