last chem test for year 11

god so help me 🙏🙏😩😩

What does kinetic theory state about the movement of gas particles?

Gases are composed of particles that are in rapid continuous random motion.

What does kinetic theory state about attraction and repulsion between gas particles?

Attraction and repulsion between particles in gases is negligible.

What does kinetic theory state about the spacing and volume of gas particles?

The particles of a gas are widely spaced so that the volume of all particles is negligible compared to the volume the gas occupies.

What type of energy do gas particles have?

The particles of a gas have kinetic energy (Ek).

How is the average kinetic energy of gas particles related to temperature?

The average kinetic energy of the particles is proportional to the temperature of the gas and is the same for all gases at the same temperature.

What does it mean when gas particle collisions are elastic?

As particles collide, they do not lose energy, slow down or cool down due to collisions.

Do all particles in a gas at a particular temperature have the same kinetic energy?

No.

Within a sample of gas at a particular temperature, gas particles have a range of kinetic energies and, as shown by the Maxwell-Boltzmann distribution.

The temperature determines the average kinetic energy of the particles, not the kinetic energy of each individual particle.

What does the area under a Maxwell-Boltzmann distribution curve represent?

The area under the curve represents the total number of particles present and therefore remains constant.

What happens to a Maxwell-Boltzmann distribution as temperature increases?

As temperature increases, the curve shifts to the right and flattens.

What are the main properties of gases explained by kinetic theory?

Gases take the shape of their container and have low density. Gases can be compressed. Gases rapidly diffuse through other gases. Gases exert pressure.

Using kinetic theory, explain why gases occupy the entire volume of their container.

Gas particles show negligible forces of attraction and are constantly moving.

They therefore do not clump together, but spread out, occupying the entire volume of their container.

Using kinetic theory, explain why gases can be compressed.

As gas particles have negligible volume and are widely spaced, there is room for them to be compressed into a smaller volume.

Using kinetic theory, explain why gases exert pressure.

When gas particles collide with their container walls, they exert pressure on the walls.

The pressure increases with the frequency and force of these collisions.

Explain why increasing the temperature of a gas increases its pressure.

Increasing the temperature of a gas will increase the average kinetic energy of the particles.

This results in a greater rate and force of particle collisions with the container walls. The pressure increases.

Explain why increasing the amount of gas increases pressure.

Increasing the amount of gas increases the number of gas particles in the same volume.

This causes more frequent collisions with the walls of the container, resulting in a greater force on the walls and therefore a higher pressure.

Explain why doubling the volume of a container decreases gas pressure.

The gas particles are more spread out and have a greater distance to travel before colliding with the container walls.

This leads to a decreased rate of collisions. The pressure decreases.

What is an ideal gas?

An ideal gas is a hypothetical gas whose particles have negligible volume and no intermolecular forces, and therefore obey the ideal gas equation under all conditions.

What are the two differences between real gases and an ideal gas?

The particles of a real gas actually do occupy a volume.

Particles of real gases do have forces of attraction between them.

Why is kinetic theory still useful for explaining real gases?

The differences are usually of little consequence when describing the behaviour of real gases and kinetic theory is therefore a useful model for explaining their properties.

Describe particles and forces in a solid using kinetic theory.

Forces between particles are quite strong. Particles are tightly packed and are only able to vibrate in fixed positions.

Why do solids have a fixed shape and volume and why are they virtually incompressible?

Particles are tightly packed and are only able to vibrate in fixed positions.

Describe particles and forces in a liquid.

The strong attractive forces between particles cause them to pack closely.

However, particles are able to move past each other within the liquid volume.

Why can liquids flow but still have a fixed volume?

Particles are able to move past each other within the liquid volume and liquids can flow to fill the bottom of a container.

However, they have a fixed volume and are essentially incompressible.

What is energy?

Energy is the capacity to do work.

What unit is energy measured in?

Joules.

What happens to the total amount of energy?

The total amount of energy always stays the same.

What is enthalpy?

The chemical energy stored in a chemical substance

What does the enthalpy of a substance include?

It includes energy stored in the chemical bonds of the substance, chemical potential energy, and energy due to particle motion, kinetic energy.

What are the system and surroundings in a chemical reaction?

The reaction mixture is the system and everything else, including the container, is the surroundings.

What happens to bonds during a chemical reaction?

Reactant bonds are broken, which requires energy. Product bonds are formed, which releases energy.

Why can the reactants and products have different amounts of chemical energy?

The reactants have a certain amount of chemical energy stored in their bonds.

The products have different bonds and so have a different amount of energy stored in them.

Why is energy either given out or taken in during a chemical reaction?

As energy must be conserved, any change in chemical potential energy must be balanced by an opposite change in some other form of energy, usually kinetic.

What effect can a chemical reaction have on the temperature of the surroundings?

Energy is either given out or taken in during the reaction. This means the temperature of the surroundings will either rise or fall.

When is a reaction endothermic in terms of bond breaking and bond forming?

If bond breaking requires more energy than bond forming will release

What happens to energy and surrounding temperature in an endothermic reaction?

Energy is taken in from the surroundings and the temperature of the surroundings decreases.

When is a reaction exothermic in terms of bond breaking and bond forming?

If bond breaking requires less energy than bond forming will release

What happens to energy and surrounding temperature in an exothermic reaction?

Energy is released to the surroundings and the temperature of the surroundings increases.

Compare the enthalpy of reactants and products in an exothermic reaction.

Reactants have a higher enthalpy than products.

What is the sign of ΔH for an exothermic reaction?

ΔH is negative.

Compare the enthalpy of reactants and products in an endothermic reaction.

Reactants have a lower enthalpy than products.

What is the sign of ΔH for an endothermic reaction?

ΔH is positive.

What is the enthalpy change or heat of reaction?

The resulting change in enthalpy that occurs during a chemical reaction

What equation is used to calculate enthalpy change?

ΔH = H(products) - H(reactants).

What is heat of combustion?

The enthalpy change obtained when a fixed amount of substance reacts with oxygen in a combustion reaction.

What is heat of fusion?

The enthalpy change that occurs during the melting of 1 mol of solid at its melting point.

What is heat of vaporisation?

The enthalpy change that occurs during the vaporization of 1 mole of a liquid at its boiling point.

What two methods can represent energy changes during chemical reactions?

Energy profile diagrams and thermochemical equations.

What is shown on an energy profile diagram?

Enthalpy, or potential energy, in kJ is on the y-axis and reaction progress or time is on the x-axis.

What is a thermochemical equation?

A chemical equation showing the enthalpy difference, ΔH, as part of the equation.

If energy is shown on the product side of a thermochemical equation, what does this indicate?

Energy is given off to the surroundings.

If energy is shown on the reactant side of a thermochemical equation, what does this indicate?

Energy is taken in from the surroundings.

Which physical changes are accompanied by energy changes?

Melting, vaporisation, sublimation, condensation and freezing are accompanied by energy changes.

Is melting endothermic or exothermic?

Endothermic. Energy is absorbed to disrupt intermolecular forces between particles.

Is vaporisation/boiling endothermic or exothermic?

Endothermic. Energy is absorbed to overcome intermolecular forces so particles can move further apart.

Is sublimation endothermic or exothermic?

Endothermic. The substance changes directly from solid to gas and energy must be absorbed.

Is condensation endothermic or exothermic?

Exothermic. The substance changes from gas to liquid and energy is released as intermolecular forces form.

Is freezing endothermic or exothermic?

Exothermic. The substance changes from liquid to solid and energy is released as intermolecular forces form.

What phase changes are endothermic?

Melting, vaporisation and sublimation. (solid to gas)

What phase changes are exothermic?

Condensation and freezing.

MEMORY TRICK: Which direction of phase changes is endothermic?

Think "going UP in freedom needs energy." Solid → liquid → gas is ENDOTHERMIC because energy must be absorbed to overcome/disrupt intermolecular forces.

MEMORY TRICK: Which direction of phase changes is exothermic?

Think "going DOWN in freedom releases energy." Gas → liquid → solid is EXOTHERMIC because intermolecular forces form and energy is released.

What happens to potential energy during an endothermic phase change?

Potential energy increases as particles move further apart and intermolecular forces are disrupted.

During melting or boiling, why doesn't the temperature increase?

The added heat energy is used to disrupt intermolecular forces rather than increase kinetic energy. Average kinetic energy therefore remains constant, so temperature remains constant.

What does temperature tell you about particles?

Temperature is related to the average kinetic energy of the particles.

On a sloped section of a heating curve, what happens to KE, PE and temperature?

Kinetic energy increases and temperature increases. Potential energy does not change because no phase change is occurring.

On a flat section of a heating curve, what happens to KE, PE and temperature?

Average kinetic energy remains constant, temperature remains constant and potential energy increases as intermolecular forces are disrupted.

What is the difference between a physical phase change and a chemical change in terms of forces/bonds?

Phase changes involve breaking and forming intermolecular forces, whereas chemical reactions involve breaking reactant bonds and forming new product bonds.

Why are energy changes associated with physical changes generally smaller than chemical changes?

Physical changes involve breaking and forming intermolecular forces which are much weaker.

Therefore, the energy changes associated with physical changes are generally smaller than those for chemical changes.

Using collision theory, explain the effect of increasing concentration on reaction rate.

Higher concentration means more reactant particles in the same amount of space.

This increases the frequency of collisions between reactant particles and therefore increases the rate of reaction.

Why does increasing gas pressure increase the rate of reaction?

As pressure increases, the space in which the gas particles are moving becomes smaller.

The gas particles become closer together, increasing the frequency of collisions and therefore increasing the rate of reaction.

Using collision theory, explain why increasing temperature increases reaction rate.

At a higher temperature, particles have more energy and move faster, increasing the frequency of collisions.

More importantly, a larger proportion of particles is able to overcome the activation energy, increasing the frequency of successful collisions.

Use a Maxwell-Boltzmann distribution to explain the effect of temperature on reaction rate.

At higher temperatures, more particles have sufficient energy to overcome the activation energy barrier.

This results in a larger proportion of successful collisions.

Where can a reaction involving a solid take place?

Any reaction involving a solid can only take place at the surface of the solid.

How does decreasing particle size affect surface area?

The smaller the pieces, the larger the surface area.

Using collision theory, explain why powdered solid reacts faster than large pieces of the same solid.

The smaller pieces have a larger surface area.

This means that there are more solid particles exposed to collide with, resulting in more frequent collisions and a faster rate of reaction.

What is a catalyst?

A catalyst is a substance that increases the rate of a chemical reaction without being used up in the reaction.

Using collision theory, explain why a catalyst increases reaction rate.

A catalyst provides an alternative reaction pathway with a lower activation energy.

A larger proportion of particles can therefore overcome the activation energy barrier, increasing the frequency of successful collisions and increasing the rate of reaction.

How does a catalyst affect a potential energy diagram?

The catalysed reaction has a lower activation energy because the catalyst provides an alternative reaction pathway with a lower activation energy.

How does a catalyst affect a Maxwell-Boltzmann distribution?

The distribution of particle energies does not change.

The activation energy is lowered, so a larger proportion of particles is able to overcome the activation energy barrier.

What is activation energy, Ea?

The minimum amount of energy particles must collide with to break the bonds between them.

According to collision theory, what must happen for a reaction to occur?

Reactant particles must collide with each other, collide with sufficient energy to overcome the activation energy and collide with the correct orientation.

What is a successful collision?

A collision in which particles have sufficient energy to overcome the activation energy and collide with the correct orientation so that a reaction can occur.

Why do some particle collisions not result in a reaction?

The particles may not have sufficient energy to overcome the activation energy or may not collide with the correct orientation.

How is reaction rate related to successful collisions?

The greater the frequency of successful collisions, the faster the rate of reaction.

What does a large activation energy mean and how does it affect reaction rate?

A large activation energy means that the bonds within the reactants must be strong and a considerable amount of energy will be required to break them.

A reaction with a large activation energy will have a slow rate.

What does a small activation energy mean and how does it affect reaction rate?

A small activation energy means that the reactant bonds are weak and it does not require much energy to break them.

The rate of such a reaction is much faster.