4.4 Concentration What does concentration mean? Write down your own definition. 07 October 2015

4.4 Concentration Increasing the concentration of reactants increases the frequency of collisions, increasing the rate of reaction. Increasing the pressure of reacting gases causes more collisions increasing the rate of reaction. 07 October 2015 A modern common rail diesel injection system operates at around 2000 times atmospheric pressure – almost 1000 times the pressure in a tyre. What advantage do you think such high pressures achieve?

Concentration Reactions in solution involve dissolved paticles that must collide before reaction is possible. The more crowded (concentrated) the solution, the faster the reaction. Collisions infrequentCollisions frequent

Marble chips are calcium carbonate. They react with acid to form a gas. calcium carbonate + hydrochloric acid  calcium chloride + water + carbon dioxide CaCO 3 (s) + 2HCl(aq)  CaCl 2 (aq) + H 2 O(l) + CO 2 (g) Acid and marble As the gas given off leaves the flask the total mass of the flask and its contents decreases slightly. Readings of the mass(g) can be taken. Typically at 1 minute intervals. CaCO 3 HCl

Investigating concentration 1.Put about 5 marble chips into the bottom of a conical flask. 2.Measure out 25 ml of acid (wear eye protection), and put into the conical flask, and put a piece of cotton wool in the neck. 3.Quickly place on the balance and take a reading, start the stopwatch. 4.Measure the mass of the conical flask every 10 seconds for 2 minutes. 5.Repeat for different concentrations.

Results Mass (g) Time (s)1M0.5M0.1M

Graph Plot a graph to show your results. Which line on the graph shows the fastest reaction? How can you tell? Mass (g) Time (s) Steep gradient Fast reaction Shallow gradient Slow reaction

Pressure Reactions involving gases are affected by the pressure of the gases present. If we cover one end of a bicycle pump and push in the plunger we increase the pressure. closer togetherWhat we are doing is squeezing the gas molecules closer together or making them more concentrated. And so - pressure speeds up gas reactions Low pressure High pressure

4.4 Concentration Increasing the concentration of reactants increases the frequency of collisions, increasing the rate of reaction. Increasing the pressure of reacting gases causes more collisions increasing the rate of reaction. 07 October 2015