A reaction has a positive enthalpy change, $\Delta H > 0$.

A student mixes $50.0\ \text{cm}^3$ of $1.00\ \text{mol dm}^{-3}$ hydrochloric acid with $50.0\ \text{cm}^3$ of $1.00\ \text{mol dm}^{-3}$ sodium hydroxide solution in a polystyrene cup. The temperature rises from $22.5^\circ\text{C}$ to $29.2^\circ\text{C}$.

Assume the density of the solution is $1.00\ \text{g cm}^{-3}$ and the specific heat capacity is $4.18\ \text{J g}^{-1}\text{K}^{-1}$.

A bomb calorimeter can be used instead of a spirit burner to measure the energy released by combustion of a food sample.

A student determines the enthalpy change for the reaction between magnesium and hydrochloric acid using a polystyrene cup calorimeter. The acid is in excess. The solution is assumed to have the same specific heat capacity as water, $4.18\ \text{J g}^{-1}\ \text{K}^{-1}$, and a density of $1.00\ \text{g cm}^{-3}$.

Temperature probes were placed in two beakers. Beaker A contained water at a higher initial temperature than the metal block added to it. Beaker B contained water at a lower initial temperature than the metal block added to it. The graph shows the temperature changes after contact.

Ethanol is burned in a spirit burner to heat $150.0\ \text{g}$ of water. The temperature of the water increases from $19.8^\circ\text{C}$ to $34.6^\circ\text{C}$. The mass of the spirit burner decreases by $0.420\ \text{g}$.

Use $c(\text{water}) = 4.18\ \text{J g}^{-1}\text{K}^{-1}$ and $M(\text{C}_2\text{H}_5\text{OH}) = 46.08\ \text{g mol}^{-1}$.

A reaction is carried out in a polystyrene cup and the temperature is recorded using a data logger. The reactants are mixed at $3.0\ \text{min}$. Extrapolation of the cooling curve gives a maximum temperature of $35.4^\circ\text{C}$ at the mixing time. The initial temperature was $22.0^\circ\text{C}$.

The total mass of solution is $80.0\ \text{g}$, $c = 4.18\ \text{J g}^{-1}\text{K}^{-1}$, and the limiting reactant has amount $0.0200\ \text{mol}$.

Sulfuric acid reacts with sodium hydroxide according to the equation:

$\text{H}_2\text{SO}_4(aq) + 2\text{NaOH}(aq) \to \text{Na}_2\text{SO}_4(aq) + 2\text{H}_2\text{O}(l)$

A student mixes $20.0\ \text{cm}^3$ of $0.400\ \text{mol dm}^{-3}$ sulfuric acid with $25.0\ \text{cm}^3$ of $1.20\ \text{mol dm}^{-3}$ sodium hydroxide. The temperature increases by $9.5\ \text{K}$. Assume the density of the final solution is $1.00\ \text{g cm}^{-3}$ and $c = 4.18\ \text{J g}^{-1}\text{K}^{-1}$.

A student determines the enthalpy change of a neutralization reaction using a polystyrene cup. The experimental value is $-48\ \text{kJ mol}^{-1}$, while a data-book value is $-57\ \text{kJ mol}^{-1}$.

The energy profile for a reaction shows the reactants at $65\ \text{kJ mol}^{-1}$, the products at $105\ \text{kJ mol}^{-1}$, and the highest point on the pathway at $180\ \text{kJ mol}^{-1}$.

The energy profile for a reaction is shown.

A student investigates the enthalpy change of combustion of ethanol using a spirit burner to heat water. The specific heat capacity of water is $4.18\ \text{J g}^{-1}\ \text{K}^{-1}$ and $M_r(\text{ethanol})=46.1$.

A thermometric titration is carried out by adding sodium hydroxide solution to hydrochloric acid in a polystyrene cup. The temperature is recorded after each addition.

In a thermometric titration, sodium hydroxide solution is added to $25.00\ \text{cm}^3$ of hydrochloric acid of unknown concentration. The sodium hydroxide concentration is $1.00\ \text{mol dm}^{-3}$. The temperature rises to a maximum when $20.0\ \text{cm}^3$ of sodium hydroxide has been added.

Assume the total mass of solution at the maximum temperature is $45.0\ \text{g}$, $c = 4.18\ \text{J g}^{-1}\text{K}^{-1}$, and the temperature rise at the maximum is $5.6\ \text{K}$.

A student dissolves ammonium nitrate in water in a polystyrene cup and records the temperature every $30\ \text{s}$. The solution is assumed to have a mass of $100.0\ \text{g}$ and specific heat capacity $4.18\ \text{J g}^{-1}\ \text{K}^{-1}$.

Two students determine the enthalpy change for the same neutralization reaction. Student A uses the maximum recorded temperature. Student B records temperatures before and after mixing and extrapolates both lines to the mixing time.

A reaction is investigated in a coffee-cup calorimeter. Solutions of potassium hydroxide and nitric acid are mixed. The density of each solution is $1.00\ \text{g cm}^{-3}$ and the specific heat capacity is $4.18\ \text{J g}^{-1}\ \text{K}^{-1}$.

Energy profiles for two reactions, X and Y, are shown on the same axes.

A student determines the enthalpy change for the reaction between magnesium and hydrochloric acid using a polystyrene cup calorimeter.

$\text{Mg}(s)+2\text{HCl}(aq)\to \text{MgCl}_2(aq)+\text{H}_2(g)$

A $0.240\ \text{g}$ sample of magnesium is added to $50.0\ \text{cm}^3$ of excess hydrochloric acid. The temperature increases from $20.4\ ^\circ\text{C}$ to $36.8\ ^\circ\text{C}$. Assume that the solution has density $1.00\ \text{g cm}^{-3}$ and specific heat capacity $4.18\ \text{J g}^{-1}\text{K}^{-1}$.

Solid ammonium nitrate dissolves in water and the temperature of the mixture decreases. The dissolving process is represented as:

$\text{NH}_4\text{NO}_3(s)\to \text{NH}_4^+(aq)+\text{NO}_3^-(aq)$

A hot piece of zinc metal is placed into cooler water in an insulated cup. The zinc cools and the water warms until both reach the same final temperature.

A student compares three physical or chemical changes using the same insulated cup and the same mass of water. The temperature change and the direction of energy transfer are summarized.

A food sample is burned under two different calorimetry conditions: an open flame heating a can of water and a sealed oxygen bomb calorimeter. The same mass of food is burned in each trial.

A student burns propan-1-ol to heat water. The experiment is repeated with different distances between the spirit burner and the copper calorimeter. The student calculates $\Delta H_c$ for each trial. $M_r(\text{propan-1-ol})=60.1$.

A spirit burner containing ethanol is used to heat $150.0\ \text{g}$ of water in a copper can. The mass of the burner decreases by $0.460\ \text{g}$ and the water temperature increases from $18.2\ ^\circ\text{C}$ to $41.7\ ^\circ\text{C}$.

Assume that all heat absorbed is absorbed by the water and that the specific heat capacity of water is $4.18\ \text{J g}^{-1}\text{K}^{-1}$.

A thermometric titration is carried out by adding aqueous sodium hydroxide to $25.0\ \text{cm}^3$ of hydrochloric acid in a polystyrene cup. Both solutions have the same concentration. The temperature is recorded after each addition.

A food sample is burned below a boiling tube containing $100.0\ \text{g}$ of water. The water temperature rises from $22.0\ ^\circ\text{C}$ to $36.5\ ^\circ\text{C}$ when $0.800\ \text{g}$ of the food is burned.

A reaction is carried out in a well-insulated calorimeter. The heat capacity of the calorimeter itself is not negligible.

$60.0\ \text{cm}^3$ of solution of density $1.00\ \text{g cm}^{-3}$ increases in temperature by $7.40\ \text{K}$. The calorimeter has heat capacity $85.0\ \text{J K}^{-1}$. The limiting reactant amount is $0.0150\ \text{mol}$.

A carbonate reacts with hydrochloric acid in a polystyrene cup. The reaction is endothermic and carbon dioxide is produced.

$\text{MCO}_3(s)+2\text{HCl}(aq)\to \text{MCl}_2(aq)+\text{H}_2\text{O}(l)+\text{CO}_2(g)$

A $1.48\ \text{g}$ sample of $\text{MCO}_3$ is added to $100.0\ \text{cm}^3$ of $0.500\ \text{mol dm}^{-3}$ hydrochloric acid. The molar mass of $\text{MCO}_3$ is $84.0\ \text{g mol}^{-1}$. The temperature decreases by $3.20\ \text{K}$.

Nitrogen and oxygen can react at very high temperatures to form nitrogen monoxide.

$\text{N}_2(g)+\text{O}_2(g)\to 2\text{NO}(g)$

This reaction is endothermic even though new bonds are formed in the product.

A student determines the enthalpy change of hydration of an anhydrous salt using a polystyrene cup calorimeter. A $3.20\ \text{g}$ sample of the salt is added to $40.0\ \text{g}$ of water. The molar mass of the salt is $160.0\ \text{g mol}^{-1}$. The corrected temperature rise is $11.2\ \text{K}$.

Two students measure the enthalpy change for the same exothermic aqueous reaction. Student A records only initial and highest temperatures. Student B records temperature every $20\ \text{s}$ and extrapolates the cooling curve back to the mixing time.

A bomb calorimeter is calibrated by burning $0.500\ \text{g}$ of benzoic acid, which releases $13.2\ \text{kJ g}^{-1}$. The temperature rise is $2.64\ \text{K}$. In a second experiment, $0.420\ \text{g}$ of a liquid fuel is burned in the same calorimeter and the temperature rise is $3.10\ \text{K}$.