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Define the rate of a chemical reaction.

The change in concentration amount or volume of a reactant or product per unit time.

State the two mathematical formulas used to calculate the rate of a reaction.

1. Rate = Amount of reactant used / Time 2. Rate = Amount of product formed / Time

State two common units used to measure the rate of reaction.

1. Grams per second (g/s) 2. Cubic centimeters per second (cm3/s)

Describe three experimental methods used to measure the rate of a reaction.

1. Measuring the volume of a gas produced using a gas syringe over time 2. Measuring the mass loss of a reaction mixture on a digital balance over time 3. Measuring the time taken for a cross beneath a flask to disappear due to a precipitate forming.

Explain Collision Theory.

For a chemical reaction to occur reacting particles must collide with each other with a minimum amount of energy known as the activation energy.

Define activation energy.

The minimum amount of kinetic energy that colliding particles must possess in order to break bonds and start a chemical reaction.

Explain how increasing the temperature increases the rate of reaction.

Particles gain thermal kinetic energy and move faster causing more frequent collisions per second. A higher proportion of colliding particles also possess energy equal to or greater than the activation energy making collisions more successful.

Explain how increasing the concentration or pressure increases the rate of reaction.

There are more reacting particles packed into the same volume of space. This increases the frequency of collisions per second leading to a faster rate of reaction.

Explain how increasing the surface area of a solid reactant increases the rate of reaction.

More particles are exposed and available on the outside to collide with other reactants. This increases the frequency of collisions per second.

What is a catalyst and how does it speed up a reaction without being used up?

A substance that increases the rate of a reaction by providing an alternative reaction pathway with a lower activation energy. It remains chemically unchanged at the end of the reaction.

Define an enzyme in biological terms.

A biological catalyst made of protein that speeds up metabolic chemical reactions inside living organisms.

What is a reversible reaction?

A chemical reaction where the products can react together to reform the original reactants; denoted by a two-way dynamic arrow.

Define dynamic equilibrium.

A state in a closed system where the forward and reverse reactions occur at the exact same rate causing the concentrations of reactants and products to remain constant.

What is a closed system in chemistry?

A reaction vessel where no reactants or products can escape into the surroundings and no outside matter can enter.

State Le Chatelier's Principle.

If a change in conditions (temperature pressure or concentration) is applied to a reversible reaction at dynamic equilibrium the position of equilibrium will shift to counteract and oppose that change.

How does increasing the temperature affect the position of equilibrium?

The equilibrium shifts in the direction of the endothermic reaction to absorb the extra heat energy and lower the temperature.

How does decreasing the temperature affect the position of equilibrium?

The equilibrium shifts in the direction of the exothermic reaction to release heat energy and raise the temperature.

How does increasing the gas pressure affect the position of equilibrium?

The equilibrium shifts towards the side of the balanced equation with the fewest moles of gas to reduce the total number of particles and lower the pressure.

How does decreasing the gas pressure affect the position of equilibrium?

The equilibrium shifts towards the side of the balanced equation with the most moles of gas to increase the total number of particles and raise the pressure.

How does changing the concentration of a reactant affect equilibrium?

If reactant concentration is increased the equilibrium shifts to the right to make more products. If product concentration is increased the equilibrium shifts to the left to make more reactants.

What is an exothermic reaction and what happens to the temperature of the surroundings?

A chemical reaction that releases thermal energy to its surroundings causing the temperature of the surroundings to increase.

What is an endothermic reaction and what happens to the temperature of the surroundings?

A chemical reaction that absorbs thermal energy from its surroundings causing the temperature of the surroundings to decrease.

What features define an exothermic reaction profile diagram?

The energy level of the products is lower than the energy level of the reactants and the overall energy change (delta H) is negative.

What features define an endothermic reaction profile diagram?

The energy level of the products is higher than the energy level of the reactants and the overall energy change (delta H) is positive.

Describe energy changes in terms of breaking and making chemical bonds.

Bond breaking is an endothermic process because energy must be taken in to break bonds. Bond making is an exothermic process because energy is released when new bonds form.

How can you calculate the overall heat energy change (delta H) for a reaction using bond energies?

Delta H = Total energy required to break bonds in the reactants - Total energy released when making bonds in the products.

How can you tell a reaction is exothermic using bond energies?

The energy released when making new bonds in the products is greater than the energy required to break the existing bonds in the reactants resulting in a negative delta H.

How can you tell a reaction is endothermic using bond energies?

The energy required to break the existing bonds in the reactants is greater than the energy released when making new bonds in the products resulting in a positive delta H.