C6 Flashcards
What is the mean rate of reaction equation?
Quantity of reactant used / time taken OR Quantity of product produced / time taken
What can the quantity of a reactant or product be measured in?
Mass in grams or by a volume in cm^3
What is the unit for rate of reaction?
g/s cm3/s
What are some factors which affect the rates of chemical reaction? (5)
- Concentrations of reactants. / Pressure in gases 2. Surface area of solid reactants 3. Temperature 4. Presence of catalysts
How does increasing the temperature increase the rate of reaction?
The particles all move faster. They are going to successfully collide. ore frequently. When they move faster, they have more energy which is needed for the reaction to happen.
How does increasing the concentration or pressure of gases increase the rate of reaction?
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How does increasing the pressure of gases (reactants) increase the rate of reaction?
There are the same number of particles in a smaller space. So the successful collisions are more frequent.
How does increasing the surface area increase the rate of reaction?
Particles have more area (exposed particles) to collide with = more frequent collisions
How does using a catalyst increase the rate of reaction?
It speeds up the reaction without being used up in the reaction itself. They usually decrease the activation energy needed by finding an alternative path.
Required practical 5 - Magnesium + HCl reaction to produce H2 gas
- Add dilute HCl to a conical flask and measure it on a mass balance. 2. Add Magnesium ribbon to acid and plug with cotton wool. 3. Start the stopwatch and record the mass at regular intervals. 4. Plot the results in a table and work out mass loss. 5. Repeat with more concentrated acids. It should show higher concentration gives a faster rate of reaction.
Required practical 5 - sodium thiosulfate and HCl to produce cloudy precipitate.
- Add dilute sodium thiosulfate to a conical flask. 2 Place a piece of paper with a black cross on it. Add HCl and start stopwatch. 3. Watch cross disappear. 4. Reaction can be repeated with reactants of different concentrations. Higher concentration means quicker reaction.
What does the collision theory say?
Collision theory says that chemical reactions can only occur when reacting particles collide with each other and have sufficient energy.
What is the activation energy?
Energy which particles must need to start a reaction.
What does increasing the concentration; pressure and surface area do to the particles?
They collide more frequently so increases the rate of reaction.
What does increasing the temperature do to the particles?
Increases the frequency of the particles and makes the particles more energetic so increases the rate of reaction.
How does a graph with a catalyst compared to a graph without?
The activation energy is lower on the graph with the catalyst.
How is a reversible reaction represented? (equation)
A +B ⇌ C + D
Give an example of how reversible reactions can be changed by changing the conditions.
When you heat ammonium chloride —> ammonia + hydrogen chloride. When you let ammonia + hydrogen cool —> ammonium chloride.
If a reversible reaction is exothermic one way; what is it the other way?
Endothermic
What occurs when a reversible reaction occurs in a closed system?
Equilibrium is reached when both reactions occur at the same rate.
What is Le Chantelier’s Principle?
If you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change.
According to Le Chantelier’s Principle; what reaction is favoured if the temperature decreases?
The exothermic reaction would be favoured so more heat is given to warm up the surroundings. More products from the exothermic reaction will be made.
According to Le Chantelier’s Principle; what reaction is favoured if you increase the pressure?
It favours the side with the least moles.
According to Le Chantelier’s Principle; what happens when you increase the concentration of the reactants?
The amount of products increase.
According to Le Chantelier’s Principle; what happens when you increase the concentration of the products?
The amount of reactants increase.
