Thermo, Kinetics, Equilbrium Practice Assessment

Front

Which way does heat energy move within a system?

Back

Heat energy flows from warmer objects to colder objects in a system.

Answer explanation

Heat always moves from something hot to cold until the temperature of the water is equal to the temperature of the item.

Think about a putting a iron into water, what happens to the water? What happens to the iron?

Front

A sample of water was heated from 50^oC to 75^oC, gaining 1050 joules. Calculate the mass of water. Specific heat of water is 4.18 J/g^oC.

Back

10.04 g

Answer explanation

q = 1050 J
m: ?

c: 4.184 J/g*C

T: 75 - 50 = 25

1050 J = m x 4.184 x 25

1050J = m x 104.6

10.04 = m

Front

How much heat energy is absorbed by a 50 g sample of iron when it is heated from 24^oC to 96^oC? The specific heat of iron is 0.449 J/g^oC.

Back

1616.4 J

Answer explanation

q = ?

m = 50g

c = 0.449 J/g*C

T = 96 - 24

q = 50 x 0.449 x (96-24)

q = 50 x 0.449 x 72

q = 1616.4J

Front

A 155 g sample of an unknown substance was heated from 25^oC to 40^oC. It absorbed 5230 J of heat energy. What is the unknown substance's specific heat?

Back

2.25 J/g^oC

Answer explanation

q = 5230 J

m = 155g

c = ?

T = 40 - 25

5230 J = 155 x c x (40-25)

5230 J = 155 x c x (15)

5230 J = 2,325 x c

2.25 = c

Front

Use Hess’s Law to calculate the heat of reaction for the following reaction: 2A + 2B → C + 2D. Use the following equations: 2A + C → D (H= +125 kJ), 2B → 2C + D (H= -35 kJ).

Back

H_rxn = +90 kJ

Answer explanation

Hess's Law states that the overall change in enthalpy (delta H) is equal to the sum of the change of its individual parts.

To solve this, add the delta H together.

Front

At what position on the heat curve does ice transition into water? Options: A, B, C, D, E

Back

B

Answer explanation

Transitions are phase changes.

On the heating curve, phase changes are the flat portions. Energy is increasing but temperature is not.

Ice turning into water is melting and would be at the first plateau, letter B.

Front

Which statement correctly describes what is happening in the reaction: H₂ (g) + I₂ (g) → energy + 2HI (g)?

Back

The reaction is exothermic because energy is being released as bonds are formed.

Answer explanation

Exothermic reactions release energy when creating bonds. This reaction is showing synthesis (A + B -> AB), which means a bond is forming.

Endothermic reactions absorb energy in order to break a bond. This would be decomposition (AB -> A + B). The single compound splits into two different things. Splitting means the bond is breaking.

Front

What is occurring at position D on the heating curve?

Back

Liquid water undergoes vaporization to become water vapor.

Answer explanation

Flat portions of the heating curve are phase changes. In this case D is showing evaporization (vaporization), going from liquid (C) to gas (E).

Water Vapor is a gas (like steam).

Front

According to the collision theory, what condition must reactant particles meet to form products?

Back

Reactant particles must collide with each other with sufficient energy to react.

Answer explanation

Collision theory explains what is required for a reaction to occur because not all collisions cause a reaction.

All reactions must:

1. Have proper orientation

2. 2. Have enough energy (activation energy)

3. 3. Have reactants collide.

Front

Why does increasing the temperature of the reactants result in increasing the reaction rate?

Back

The reactant particles have more energy and will collide more frequently.

Answer explanation

Temperature translates to heat energy. The more energy something has, the more it moves. If the temperature increases, movement increases, which causes the reactants to collide more frequently.