Rates of Reaction and Reversible Reactions

What is rate of reaction?

The rate of a reaction is a measure of how quickly a reactant is used up, or a product is formed

What is the collision theory?

• reactant particles must collide with each other

• the particles must have enough energy for them to react which is the activation energy

What is a collision that produces a reaction called?

A successful collision

What is the activation energy

amount of energy needed for a collision to be successful. It is different for different reactions.

How do you calculate the mean rate of reaction?

mean rate of reaction= quantity of reactant used/ time taken

What are the patterns on a graph?

• The steeper the line, the greater the rate of reaction

• Fast reactions- seen when the line becomes horizontal- finish sooner than slow reactions

What is the collision theory?

• rate of chemical reaction depends on collision frequency of reacting particles. The more collisions, the faster the rate of reaction

• Energy is transferred during a collision, Particles have to collide with enough energy for collision to be successful

What is the activation energy?

The minimum amount energy that particles need

What are the factors that increase the number of collisions?

• temperature

• conc of a solution

• surface area

• The presence of a catalyst

• pressure of gas

How does the rate of reaction increase?

Increasing the number of successful collisions

Why does pressure of gas increase rate?

• Increasing pressure is like increasing the concentration

• increases frequency of collisons

• Overall increases the rate of reaction

Why does increasing temp increase the rate?

• increases frequency of collisions

• increases energy of reactant particles meaning a greater proportion of particles will have more energy than the activation energy that is needed

• Leading to more successful collissions

• Overall increasing rate of reaction

Why does increasing concentration of dissolved reactants increase rate?

• increasing conc increases frequency of collisions

• Overall, increasing the rate of reaction

How does increasing surface area increase the rate?

• this is often done by breaking up solids into smaller lumps e.g powders

• this increases surface area to volume ratio making sure that more particles are exposed to attack

How does a Catalyst increase the rate?

• catalysts are substances that increase rate of chemical reaction wihtout being used up in the process

• they lower the activational energy

How do reversible reactions work?

If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction. The same amount of energy is transferred in each case

What is an equilibrium?

When a reversible reaction occurs in apparatus which prevents the escape of reactants and products, equilibrium is reached when the forward and reverse reactions occur at exactly the same rate

What is an equilibrium position?

a measure of the concentrations of the reacting substances at equilibrium

How can energy transfers that take place in exothermic and endothermic reactions be measured?

By monitoring the temperature of the surroundings

What happens to energy during chemical reactions?

It is conserved

What’s the background to the Haber process?

Nitrogen gas is reacted with hydrogen gas to make ammonia gas. The forward reaction is exothermic

What'‘s Le Chatelier’s principle?

The equilibrium position can be changed by changing the reaction conditions through:

• changing pressure

• changing conc

• changing temp

What happens if conditions of an equilibrium is changed?

• Changing the conditions in which a reversible reaction is taking place can affect the position of equilibrium

What happens when you change pressure?

• decrease- position of equilibrium will shift towards the side of the reaction that produces most gas molecules

• increase- position of equilibrium will shift to favour the reaction that produces the fewest gas molecules

What happens if you change the temperature in a reversible reaction?

• temp decrease- position of equilibrium shift in the exothermic direction

• temp increase- position of equilibrium shifts in the endothermic direction

What happens if you change the concentration in a reversible reaction?

If the concentration of a reactant (on the left) is increased, the equilibrium position moves in the direction away from this reactant, and so more of the products are produced (on the right). If one of the products is removed from a reaction (on the right), then the position of equilibrium moves to the right to make more of that product

What happens if you change the pressure in a reversible reaction?

If the pressure is increased in a reaction involving gases, the equilibrium position moves in the direction of the fewest molecules of gas, to reduce the pressure

What’s sodium thiosulfate practical?

1. Pour 50 cm3 of sodium thiosulfate solution into a conical flask.

2. Put the conical flask on a black cross drawn on a piece of paper.

3. Pour 10 cm3 of hydrochloric acid into the conical flask and start a timer.

   Stop the timer when the cross can no longer be seen.

4. Repeat the experiment at different temperatures.