Chem Unit 7

Four substances at the same temperature absorb equal amounts of energy. The specific heats of the four substances are 1.01 J/g °C, 0.38 J/g °C, 0.13 J/g °C, and 2.00 J/g °C. What is the specific heat value of the substance that will have highest increase in temperature?

0.13 J/g °C

Some thermodynamic properties of ethanol are listed in the table. Thermodynamic Properties Property Value c (solid) 0.5 J/g °C c (liquid) 1.0 J/g °C c (gas) 2.0 J/g °C Melting Point −114 °C Boiling Point 78 °C How much heat is released when 50.0 g of ethanol cools from 90 °C to 79 °C?

1,100 J

If 832 joules of energy are required to raise the temperature of a sample of aluminum from 20.0 °C to 97.0 °C, and the specific heat of aluminum is 0.90 J/(g °C), what is the mass of the aluminum?

12.0 g Al

How many joules are absorbed when 86.8 grams of water is heated from 40.0 °C to 86.0 °C?

16,700 joules

The table shows the concentration of a reactant in the reaction mixture over a period of time. Reactant Concentration Time Concentration 0s 1.8 M 210s 1.2 M 450s 0.8 M 580s 0.6 M 720s 0.4 M What is the average rate of the reaction over the first 580 seconds?

2.0 × 10−3

What change would shift the equilibrium system to the left? A(g) + B(s) + Energy ⇌ 3C(g)

Adding more of gas C to the system

What is a substance that reduces the amount of activation energy in a chemical reaction called?

Catalyst

A certain reaction is exothermic in the forward direction. The reaction has more moles of gas on the product side. Which of the following stresses would increase the yield of the products (shift right)?

Decreasing the pressure

Which of the following happens during an exothermic chemical change?

Heat is released.

In an experiment, hydrochloric acid reacted with different volumes of sodium thiosulfate in water. A yellow precipitate was formed during the reaction. A cross drawn at the base of each flask became gradually invisible due the formation of this yellow precipitate. The time taken for the cross to become invisible was recorded. A partial record of the experiment is shown. Experimental Record Flask Volume of HCl Volume of Sodium Thiosulfate Volume Water 1 10 mL 10 mL 40 mL 2 10 mL 20 mL 30 mL 3 10 mL 30 mL 20 mL 4 10 mL 40 mL 10 mL Time 14 ? ? ? Based on your knowledge of factors that affect the rates of chemical reactions, predict the trend in the last column of the experimental record. Use complete sentences to explain the trend you predicted. You do not have to determine exact values for time; just describe the trend you would expect (increase or decrease) and why it occurs.

I believe the time would go up, the first volume stays the same, and sodium thiosulfate slowly increases as the volume of water goes down. When looking at this you can see the concentration of the reactants increase, which typically means the reaction rate will also increase.

What stress will shift the following equilibrium system to the left? 2SO2(g) + O2(g) ⇌ 2SO3(g); ΔH= -98.8 kJ/mol

Increasing temperature

You are given a reversible reaction in aqueous solution, 2A + B ⇌ C + D, and know that the forward reaction is exothermic. Which conditions would shift the equilibrium to favor the creation of more product and why?

Increasing the concentration of A and B and decreasing the temperature because lowering the temperature shifts the equilibrium farther right

Which statement is correct about the rate of a chemical reaction?

It increases when the concentration of reactants increases.

Which statement is correct about the rate of most chemical reactions?

It increases when the temperature increases.

Which of the following is true for the equilibrium constant of a reaction?

It is a ratio of the concentrations in a reaction.

During an endothermic reaction, ΔH for the reactants was −600 kJ/mol. Which of the following statements is correct about the ΔH for the products?

It is greater than −600 kJ/mol because the amount of energy required to break bonds is less than the amount of energy released in forming bonds. close

How does a catalyst increase the rate of a reaction?

It provides a lower activation energy for the reaction.

The volume of a reaction vessel with gaseous reactants is lowered to one-fourth of its original volume. What will happen to the rate of the reaction?

It will increase because the concentration of the reactants increases.

A chemical equilibrium between gaseous reactants and products is shown N2(g) + 3H2(g) ⇌ 2NH3(g) How will the reaction be affected if the pressure on the system is increased?

It will shift toward the product side as there are a fewer number of moles of gas on the product side.

The table shows the conditions during two trials of a reaction. Reaction Conditions Trial Temperature Catalyst 1 30 °C Platinum 2 30 °C Platinum Assuming that all other conditions remain the same during the two trials, which of the following is true for the reaction?

More reactant particles meet the activation energy requirement in Trial 2 than Trial 1.

Which statement is true about the potential energy diagram for an exothermic reaction?

Products have less potential energy than reactants.

The specific heats of two natural substances are shown in the table. Specific Heat Natural Substance Specific Heat Wet Mud 2.5 J/g °C Sandy Clay 1.4 J/g °C A pile of wet mud and a pile of sandy clay of equal masses were placed next to each other on a sunny day .If the temperature of each pile was equal in the afternoon, which substance is likely to show a higher temperature after a few hours and why?

Sandy clay, because it requires less energy to increase its temperature.

According to Le Châtelier's principle, how will an increase in pressure affect a gaseous equilibrium system?

Shift it toward the side with lower total mole concentration

Match the action to the effect on the equilibrium position for the reaction N2(g) + 3H2(g) ⇌ 2NH3(g). Removing ammonia Removing hydrogen gas Adding a catalyst

Shift to the right No effect Shift to the left

The substances below are listed by increasing specific heat capacity value. Starting at 30.0 °C, they each absorb 100 kJ of thermal energy. Which one do you expect to increase in temperature the most?

Silver, 0.239 J/(g °C)

Which of the following represents the quantity of heat required to raise the temperature of one gram of a substance by one degree Celsius?

Specific heat capacity

According to the collision theory, what two factors must be true for a given collision to successfully create products?

Sufficient speed and correct orientation of particles

A reaction mixture is at equilibrium. What happens when the amount of one of the reactants is increased?

The amount of the product also increases.

When zinc reacts with hydrochloric acid, it produces hydrogen gas. As the reaction proceeds, why does the rate of production of hydrogen gas decrease?

The concentration of the reactants decreases.

What will most likely happen when a component is removed from a reaction system at equilibrium?

The equilibrium system will shift to replace some of what was removed.

Nitrogen dioxide gas is dark brown in color and remains in equilibrium with dinitrogen tetroxide gas, which is colorless 2NO2(g) ⇌ N2O4(g) When the mixture was moved from room temperature to a higher temperature, the mixture turned darker brown. Which of the following conclusions about the mixture is true?

The forward reaction is exothermic.

Linda performed the following trials in an experiment. Trial 1: Heat 30.0 grams of water at 0 °C to a final temperature of 40.0 °C. Trial 2: Heat 40.0 grams of water at 30.0 °C to a final temperature of 40.0 °C. Which statement is true about the experiments?

The heat absorbed in Trial 1 is about 3,347 J greater than the heat absorbed in Trial 2.

Consider the following equilibrium reaction having gaseous reactants and products. 4HCl + O2 ⇌ 2H2O + Cl2 Which of the following would result from increasing only the concentration of oxygen?

The rate of forward reaction increases.

Which of the following happens when a reaction reaches dynamic equilibrium in a closed system?

The rate of the forward reaction equals the rate of the reverse reaction.

CH4(g) + 2O2(g) → CO2(g) + 2H2O(l): ΔH = −890 kJ

The reaction of one mole of oxygen (O2) releases 445 kJ of energy.

What happens when the temperature or pressure of a reaction system at equilibrium is altered?

The system will try and offset the change.

During an experiment, solid iodine was placed in a sealed container. The container was gradually heated and purple-colored vapors of iodine formed were observed. Describe this system when it reaches phase equilibrium.

There is no net change in solid or vapor iodine amounts preset in the system. This is because the rate of forward and reverse relations are equal since the system is in equilibrium.

According to Le Châtelier's principle, an increase in temperature will shift the equilibrium position toward the products in an endothermic reaction.

True

If the amount of energy required to break bonds in the reactants is less than the amount of energy released in forming bonds in the products, the chemical reaction is endothermic.

True